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Unformatted text preview: Eumetazoans
• All animals except sponges belong to the Eumetazoa, the animals with true tissues. • The oldest eumetazoan clade is the Radiata, animals with radial symmetry and diploblastic embryos. • The two phyla of Radiata, Cnidaria and Ctenophora, may have had separate origins from different protozoan ancestors. Key terms to know by the end of this presentation: Radial symmetry Nematocysts Polyp Medusa Oral end Aboral end Tentacle Manubrium diploblastic tissue grade of organization gastrodermis Phylum Cnidaria: Cnidarians have radial symmetry, a gastrovascular cavity, and cnidocytes
• The cnidarians (hydras, jellies, sea anemones, and coral animals) have a relatively simple body construction. • They are a diverse group with over 10,000 living species, most of which are marine. • The basic cnidarian body plan is a sac with a central digestive compartment, the gastrovascular cavity. Phylum Cnidaria: Composed of Three Classes
• Major difference between the classes is which of the two body plans is present or dominant • There are also other morphological distinctions you will see in the laboratory • This basic body plan has two variations: the sessile polyp and the floating medusa.
• The cylindrical polyps, such as hydras and sea anemones, adhere to the substratum by the aboral end and extend their tentacles, waiting for prey. • Medusas (also called jellies) are flattened, mouth-down versions of polyps that move by drifting passively and by contacting their bell-shaped bodies.
Fig. 33.4 • Muscles and nerves exist in their simplest forms in cnidarians. • Cells of the epidermis and gastrodermis have bundles of microfilaments arranged into contractile fibers.
• True muscle tissue appears first in triploblastic animals. • When the animal closes its mouth, the gastrovascular cavity acts as a hydrostatic skeleton against which the contractile cells can work. • Movements are controlled by a noncentralized nerve net associated with simple sensory receptors that are distributed radially around the body. Phylum Cnidaria: Composed of Three Classes
• Class Hydrozoa (hydro= water, zoon = animal) Hydra Gonionemus Obelia Physalia Class Hydrozoa
• Solitary or colonial animals • Polyp is the dominant stage • Medusa stage is absent or reduced • Medusae (when present) has a velum (iris-like diaphragm that is used to create a powerful jet for movement) • Freshwater or marine Fig. 33.5 Nerve nets in cnidarians Reproduction in Class Hydrozoa
Hydra has unusual sexual structures for a cnidarian Male hydras produce sperm in spermaries-- small conical outgrowths from the side of the body Females have ova in their ovaries (more rounded in shape) Sperm are released travel through water to ovaries embryo develops in female ovary after 7-10 days young, miniature hydra is released. Most hydrozoans have a medusa stage
Gonionemus: marine hydrozoan Velum: thin, muscular membrane extending inward from the margin of the umbrella-like bell VELUM is only found in members of Class Hydrozoa!! ** One can use this to distinguish hydrozoan medusae from the jelly fish of Class Scyphozoa Most hydrozoans have a medusa stage
Medusa swims with convex side (aboral) upwards and with the tentacles facing downward Gullet leads from the mouth to the GV cavity at the base of the manubrium Canals lead from the large cavity at the base to the base of the bell and to smaller channels in the tentacles: ENTIRE system makes up the GV cavity Most hydrozoans have a medusa stage
Gonionemus: sexes are separate Gonads are located along radial canals Eggs and sperm are released and fertilization occurs externally Colonial hydrozoans
Hydra and Gonionemus are solitary! Most hydrozoans are colonial Obelia is a common colonial hydrozoan found on both Atlantic and Pacific Coasts of North America =(gonangonium) (hydranth) **The entire colony is covered by a sheath called PERISARC Hydrotheca = part of the perisarc that surrounds hydranth Gonotheca = part of the perisarc that surrounds gonotheca Reproduction in Obelia
Budding of medusae from the gonangia and their release into water Medusae then reproduce sexually and the zygote develops into a swimming ciliated larva called a PLANULA The planula fastens itself to a surface, then develops into a polyp and eventually into a complete colony Physalia: Portuguese man-of-war
Floating colonial hydrozoan: colony of polyps like Obelia Some of the polyps have taken on body shapes to better specialize in one function for the colony Feeding and reproductive polyps are present Specializations: Specialized defensive polyps (long tentacles covered with nematocysts)– catch prey and ward off predators One giant, gas-filled polyp (keeps colony afloat in high seas) Full grown Physalia can be 2 to 4 feet long! Class Scyphozoa
• So-called “jelly fish” • Polypoid (shaped like a polyp) is minute or lacking • Scyphozoan medusae can be more than 2 m in diameter, although most are much smaller • Cyanea can grown tentacles as long as blue whales! Aurelia: common coastal jellyfish
Medusa reproduce sexually Gives rise to a planula larva, which forms polyp Polyp reproduces asexually and forms immature medusae called EPHYRAE, which later develop into mature medusae Class Anthozoa
Corals and sea anenomes Have only polyp stage and have a flower-like appearance Can be distinguished from other cnidarian classes because GV cavity is partitioned by mesenteries or septa that are inward extensions of body wall Sea anenomes: Class Anthozoa
Aiptasia Contains several bands of longitudinal muscles and several bands of circumferential muscles along with a non-centralized nerve net This sea anenome is translucent when hungry! Visualize septa and pharynx • Summary: Hydrozoa, Scyphozoa, and Anthozoa. • The three cnidarian classes show variations on the same body theme of polyp and medusa. Fig. 33.6 Variations on life cycles of cnidarians Fig. 32.4 Phylum Platyhelminthes: Flatworms are acoelomates with gastrovascular cavities
• There are about 20,000 species of flatworms living in marine, freshwater, and damp terrestrial habitats.
• They also include many parasitic species, such as the flukes and tapeworms. • Flatworms have thin bodies, ranging in size from nearly microscopic to tapeworms over 20 m long!! • Flatworms and other bilaterians are triploblastic, with a middle embryonic tissue layer, mesoderm, which contributes to more complex organs and organs systems and to true muscle tissue. • While flatworms are structurally more complex than cnidarians, they are simpler than other bilaterans.
• Like cnidarians, flatworms have a gastrovascular cavity with only one opening (and tapeworms lack a digestive system entirely and absorb nutrients across their body surface). • Flatworms have a recognizable head and tail • More properties of flatworms:
• Lack a body cavity between the outer body wall and gut • Unlike other bilaterians, flatworms lack a coelom. They are ACOELOMATES • We say these animals have ORGAN LEVEL of Complexity • More properties of flatworms:
• Like the cnidarians, the digestive tract is called INCOMPLETE in that it has only one entrance • Some of the parasitic flatworms are specialized for living within the gut of their host and absorb their nutrients when they have been digested by their host • These specific flatworms lack a digestive tract Flatworms are divided into four classes: Turbellaria, Monogenia (not covered in lab manual), Trematoda, and Cestoidea. Turbellarians are nearly all free-living (nonparasitic) and most are marine.
• Planarians, members of the genus Dugesia, are carnivores or scavengers in unpolluted ponds and streams. Planarians and other flatworms lack organs specialized for gas exchange and circulation.
• Their flat shape places all cells close to the surrounding water and fine branching of the digestive system distributes food throughout the animal. • Nitrogenous wastes are removed by diffusion and simple ciliated flame cells help maintain osmotic balance.
• Quiz: Where is dorsal? Where is ventral? A closer look: Planaria BODY PLAN A closer look: Planaria BODY PLAN A closer look: Planaria BODY PLAN Properties of Class Turbellaria Model organism: Planaria
Small freshwater animals called planarians Move by ciliary mucus mechanism: cilia found on ventral side Small glands that secrete mucus lubricant to help the worm glide smoothly along a substratum Mouth usually ventral Body undivided Development is usually direct (= no larval A closer look: Planaria BODY PLAN Planarians and other flatworms lack organs specialized for gas exchange and circulation.
• Their flat shape places all cells close to the surrounding water and fine branching of the digestive system distributes food throughout the animal. • Nitrogenous wastes are removed by diffusion and simple ciliated flame cells help maintain osmotic balance.
• Quiz: Where is dorsal? Where is ventral? • Planarians move using cilia on the ventral epidermis, gliding along a film of mucus they secrete.
• Some turbellarians use muscles for undulatory swimming. • A planarian has a head with a pair of eyespots to detect light and lateral flaps that function mainly for smell. • The planarian nervous system is more complex and centralized than the nerve net of cnidarians.
• Planarians can learn to modify their responses to stimuli. • Planarians can reproduce asexually through regeneration.
• The parent constricts in the middle, and each half regenerates the missing end. • Planarians can also reproduce sexually.
• These hermaphrodites cross-fertilize. • The monogeneans (class Monogenea) and the trematodes (class Trematoda) live as parasites in or on other animals.
• Many have suckers for attachment to their host. • A tough covering protects the parasites. • Reproductive organs nearly fill the interior of these worms. • Trematodes parasitize a wide range of hosts, and most species have complex life cycles with alternation of sexual and asexual stages.
• Many require an intermediate host in which the larvae develop before infecting the final hosts (usually a vertebrate) where the adult worm lives. • The fluke Schistosoma infects 200 million people. Trematode Form and Function
• Most species are elongated and dorso-ventrally flattened; but some have thick fleshy bodies and some are round in section • There are typically 2 suckers, an anterior oral sucker surrounding the mouth, and a ventral sucker sometimes termed the acetabulum, on the ventral surface (Two branched intestine) Clonorchis: the human liver fluke
• Clonorchis: the human liver fluke
• Clonorchis: the human liver fluke
• Clonorchis: the human liver fluke
• Homework: Label Miracidia
• A swimming sac-like larva, carrying a number of germinal cells from which will arise subsequent generations of organisms (e.g. sporocysts, etc.) • Possess an apical gland - empties rapidly during penetration and is thought to release proteolytic enzymes Miracidia
• After penetration, the miracidium normally sheds its ciliated covering and elongates to become a sporocyst • A pair of glands called penetration or adhesive glands secrete a mucoid material which appears to assist in the attachment to snail host tissue Miracidia cont.
Miracidium penetrating a host • There is some evidence that miracidia are attracted to its molluscan host via chemotaxis • Miracidia of many species will not hatch until they are eaten by the appropriate snail, after which they penetrate the snail’s gut Cercariae Tegument
Metabolically active area • The tegument is essentially a syncytial epithelium - distal cytoplasm is continuous, with no intervening cell membranes • It comprises an outer, anucleate layer of cytoplasm connected by cytoplasmic strands to the nucleated portions of the cytoplasm
• In addition to its protective role, the tegument has numerous other functions
• absorption of nutrients; although they have a well developed gut, materials can be brought in via the tegument • synthesis and secretion of various nutrients • excretion and osmoregulation • sensory role (due to the presence of various sensory organs) Muscular System
• The bodies and parts of bodies of flatworms are often seen to expand, contract, and twist, and this movement indicates the presence of muscles • These muscles lie in groups or layers primarily near the body surface as longitudinal or circular fibers • Some fibers do occur with the suckers Nervous System
• Paired ganglia at the anterior end of the body serve as the brain; from here, nerves extend anteriorly and posteriorly • Most sensory receptors are lacking among the adults; they do have tangoreceptors, receptors sensitive to touch • Larval stages have many kinds of sensory receptors, important for locating hosts in the environment • Many have light receptors and chemoreceptors Most monogeneans are external parasites of fishes
• Their life cycles are simple, with a ciliated, freeliving larva that starts an infection on a host. • While traditionally aligned with trematodes, some structural and chemical evidence suggests that they are more closely related to tapeworms. Fig. 32.4 • The blood fluke Schistosoma infects 200 million people, leading to body pain, anemia, and dysentery. Fig. 33.11 Tapeworms (Class Cestoda) are also parasitic.
• The adults live mostly in vertebrates, including humans. • Suckers and hooks on the head or scolex anchor the worm in the digestive tract of the host. • A long series of proglottids, sacs of sex organs lie posterior to the scolex. • Tapeworms absorb food particles from their hosts. Tapeworms continued
• Possess scolices with 4 suckers
• Most tapeworms of birds and mammals belong to this group Taenia solium (human pork tapeworm)
• Humans are the only known natural definitive hosts • It is common in humans in areas where raw or improperly cooked pork is a regular element of the diet • The scolex is armed with 2 circles of hooks • The hooks are of 2 sizes and alternate in the 2 circular rows Life cycle
• Proglottids may rupture either in the host intestine or after it leaves the host • When eggs are ingested by pigs, the liberated oncospheres, using their hooks and penertration glands, penetrate the intestinal wall • Then gain access to the circulatory system, and are carried by the blood or lymph to muscles, viscera and other organs, where they develop into cysticerci Life cycle cont. • Each cysticercus, contains a single invaginated scolex • When infected, or pork is consumed by a human, the scolex evaginates and attaches to the intestinal wall • There the parasite develops to maturity in about 2-3 months Symptoms and Diagnosis cont. •While common sites for infection by cysticerci are the skeletal muscles and the brain, they can develop in practically any organ of the body, including the eyes and lungs, and heart Section of a human brain containing numerous Taenia cysticerci. Mature proglottids, loaded with thousands of eggs, are released from the posterior end of the tapeworm and leave with the host’s feces.
• In one type of cycle, tapeworms eggs in contaminated food or water are ingested by intermediary hosts, such as pigs or cattle. • The eggs develop into larvae that encyst in the muscles of their host. • Humans acquire the larvae by eating undercooked meat contaminated with cysts. • The larvae develop into mature adults within the human. Young Proglottids
• Forms by transverse budding in the neck region • Organs of excretion (FLAME CELLS) • Nervous system (longitudinal nerve cords) • Organs of reproduction • A tapeworm is very similar to a colony of individual flatworms that live attached in a line Mature Proglottids
• Everything but the sex organs degenerates • Male reproductive organs mature first, then the female organs • Proglottids are generated from the neck end: • Quiz: where are the oldest proglottids? • Male proglottids are found in the middle, proglottids found with all of the vegetative organs found near the neck Cestode reproduction
• ova in hermaphroditic proglottids are fertilized by sperm from some other tapeworm or from a proglottid located farther anteriorly • self-fertilization and cross-fertilization are possible • Some of the proglottids eventually break off and are released from the host’s digestive tract with the feces • Some of the zygotes are eaten by the intermediate host: hatched larva penetrate intestinal wall travels by way of the lymphatic and blood vessels skeletal muscle Some key terms to know by the end of this presentation:
Tube within a tube Cuticle (all of the layers) Complete digestive system Buccal cavity Noncompressible fluid Pseudocoelom Longitudinal muscles Circular muscles C. elegans A. lumbricoides Hookworms W. Bancrofti L. Loa Dracunculus Anisakis Phylum Nematoda (Part I)
• Basic properties of nematodes • Anatomy of model system nematodes: Caenorhabditis elegans and Ascaris lumbricoides • Properties of the pseudocoelom • Properties of the cuticle • Musculature and movement • Several life cycles of parasitic nematodes Phylum Nematoda (Greek nematos = thread)
• Roundworms = nearly circular cross section • 90,000 Species identified • Cross section is circular because the worm is holding in so much pressure that their sides bulge equally in all directions • The body of a nematode has as much internal pressure as your own aortic artery! • High pressure affects most of the nematode’s morphology and behavior High pressure lifestyle is successful!
• Marine mud ecosystems may contain 4 million nematodes per square meter • Some terrestrial ecosystems have nematode populations estimated at billions per acre • some species are free living, while other are parasitic in plants or animals Nematodes are bilaterally symmetric and triploblastic
• “tube-within-a-tube” body form • cavity (pseudocoel) between the wall of the gut and the body wall • outer wall of the cavity is bounded by tissue derived from mesoderm and the inner wall by tissue derived from endoderm Quiz: what would the wall of the cavity look like if it were a true coelom? The Pseudocoel
• Filled with fluid or a gelatinous substance • major function is circuclation and distribution of material throughout the body and also as a hydrostatic skeleton functioning in locomotion (high internal pressure comes in handy) • complete digestive tract: anus is separate from the mouth and that food travel through the tract in only one direction General Characteristics of Nematodes • Body elongate, cylindrical, and tapered at both ends • Body design is a tube within a tube, the outer tube being the body wall and underlying muscles and the inner tube being the digestive tract • Between the tubes is the fluid-filled pseudocoelom, in which the reproductive system and other structures are found; the pseudocoelom is filled with hemolymph General Characteristics cont.
Although there are some structural differences between pseudocoeloms and coeloms, they confer many of the same advantages: • A space within the body cavity allows for the reproductive and digestive systems to evolve more complex shapes and functions • A fluid lined chamber offers protection to the gut and other organs; acts as a cushion • The fluid filled body cavity acts as a skeleton hydrostatic skeleton, providing support and rigidity for a soft bodied animal The Pseudocoel and the Hydrostatic Skeleton
• enclosure of noncompressible fluid • ability of muscles to apply pressure to that fluid • transmission of the pressure in all directions in the fluid as a result of the incompressibility SIMPLE CASE: contraction of circular muscles and relaxation of longitudinal muscles make an animal thinner and longer; relaxation of the circular muscles and contraction of the longitudinal muscles make the thicker and shorter. PROBLEM: Nematodes only have longitudinal muscles!!! Nematodes do not have circular muscles
So where does this stretching and compression act against? Alternating contraction and relaxation in dorsal and ventral muscles impels the body in a series of curves in a single, dorsoventral plane, producing the S-shaped motion observed How could one improve the efficiency of the system? Nematode movement General Characteristics cont. • Sexual dimorphism is evident: at the curved posterior end of the male there is a copulatory organ as well as other specialized organs; males are usually smaller than females Cuticle
• An elastic cuticle covers the body surface of nematodes; it is periodically molted • The presence of enzymes in the cuticle indicates that it is metabolically active and not an inert covering • Specialized structures such as spines, bristles, warts, papillae, and ridges may be present on the cuticle; these structures may be sensory and some may aid in locomotion Cuticle
•The cuticle not only covers the entire external surface, but it also lines the buccal cavity, esophagus, rectum, cloaca, vagina, and excretory pore • Cuticle consists of 4 basic layers: epicuticle, exocuticle, mesocuticle, and endocuticle Ascaris lumbricoides
•A large intestinal roundworm of humans; females can be lengths of 30 cm! •The posterior end of the female is strait, while that of the males curves ventrally. • The female can deposit about 200,000 eggs daily! • Uterus may contain up to 27 million eggs at one time!
The anterior end of Ascaris lumbricoides. Notice the three prominent "lips". Female and male Ascaris lumbricoides Ascaris Life Cycle Life Cycle of Ascaris lumbricoides
• Adult worms live in the lumen of the small intestine and get nourishment from semidigested food in the host • Copulation occurs here and eggs are passed with the feces • The outer, albuminous coat of the egg is brown in color due to bile pigment absorbed from the feces • The zygote does not begin development until the egg has reached the soil Life Cycle Continued
• Eggs are fairly resistant to dessication and low temperatures • With proper temperatures and oxygen levels the embryo molts at least once in the shell and develops to an infective larva • Eggs can remain viable in the soil for 2 years Epidemiology of Ascaris infections
• Distribution of A. lumbricoides is worldwide, but it is prevalent in warmer climates • It depends upon poor sanitation for its proliferation • It is most prevalent in children; they are exposed to contaminated soil, do not wash before eating, put hands in mouth, etc. Symptoms of Ascaris infections
• Most cases of ascariasis are symptomless
• The most frequent symptom is upper abdominal discomfort • Little damage results from larval penetration of the host’s mucosa • However, aberrant larvae migrating in such organs as the spleen, liver, lymph nodes, and brain usually result in an inflammatory response • Also, larvae escaping from capillaries in the lungs and entering the respiratory system cause small, hemorrhagic foci accompanied by coughing, fever, and difficulty in breathing Symptoms continued
Worms sometimes cause mechanical blockage of the intestinal tract • Also, worms may penetrate the intestinal wall or appendix causing local hemorrhaging • Overcrowding may also lead to wandering; worms can enter the appendix and cause blockage; worms have been known to migrate all he way to the anus • Some worms migrate anteriorly and have been known to block pancreatic and bile ducts; others have gotten into the stomach and some even as far as the esophagus and tracheae Hookworm
•The most serious stage of hookworm infection occurs when the parasites become established in the host’s intestine during the intestinal phase. • Upon reaching the small intestine, young worms use their buccal capsules and teeth to burrow through the mucosa, where they begin to feed on blood. Humans become infected with animal hookworms by contact with soil upon which infected dogs have defecated • The feet, arms, and face are the most common sites of infection • Red, itchy papules develop at the invasion site, and the migratory paths of the larvae appear as slightly elevated ridges Wuchereria bancrofti
• This filarial worm is parasitic only to humans
• It is characterized by extensive enlargement of extremities • Ancients likened the thickened skin to that of elephants, hence the misnomer elephantiasis (which literally means “caused by elephants” rather than “like elephants”) Life Cycle of Wuchereria
• Adults lived coiled together in the major lymphatic ducts • Here the lymph vessels and glands become blocked causing edema • In time, the accumulation of connective tissue cells and fibers contributes to the enlargement of limbs, scrotum, and other extremities Adult Loa loa visible under the skin Adult Loa loa coilied under the conjunctival epithelium of the eye Dracunculus Dirofilaria immitis Dog heartworm Anisakis life cycle Some key terms to know by the end of this presentation (Phylum Nematoda, Part II):
Tube within a tube Cuticle (all of the layers) Complete digestive system Buccal cavity Noncompressible fluid Pseudocoelom Longitudinal muscles Circular muscles C. elegans A. lumbricoides Hookworms W. Bancrofti L. Loa Dracunculus Anisakis Nematode digestive system
• Many nematodes have anaerobic metabolism • Some are obligate aerobes • Alimentary canal consists of: • mouth, • muscular pharynx, • long nonmuscular intestine, • a short rectum, and a • terminal anus. Nematode digestive system
Food material pharynx (contraction) intestine (relaxation) Intestine is one layer thick, food moves by body movements and by additional food being passed into the pharynx Defecation: muscles pull anus open, and explusive force applied by the pseudocoelomic pressure Nematode nervous system
Ring of nerve tissue and ganglia around the pharynx gives rise to small nerves to the anterior end and to two nerve cords (one dorsal and one ventral) Sensory papillae are concentrated around the head and tail. Amphids are a pair of sensory organs Parasitic nematodes have reduced amphids, but have a bilateral pair of phasmids Amphids 1.Intestine 2.Vagina 3.Uterus 4. Uterus 5. Oviduct 6. Ovaries Female Cross section 1. Cuticle and hypodermis 2. Longitudinal muscle layer 3. Ovary 4. Oviduct 5. Uterus 6. Intestine Male Dissection 1. Cuticle and hypodermis 2. Longitudinal muscle layer 3. Vas deferens 4. Testis 5. Lateral line with excretory canal 6. Intestine 7. Pseudocoelom Some key terms to know by the end of this presentation (Phylum Annelida, Part I):
Segment Annuli Metamerism Chitinous setae Parapodia Closed blood system Gills Parapodia nephridia Fun facts about Earthworms
• Aristotle called them “intestines of the soil” • Darwin in The Formation of Vegetable Mould Through the Action of Worms • Enrich the soil by bringing subsoil to the surface and mixing it with the topsoil Fun facts about Earthworms
• Darwin estimated that 10-18 tons of dry earth per acre pass through the intestines of earthworms annually • Brings potassium and phosphorus up to the surface and adds nitrogenous products • Aerates the soil, brings leaves and other organics close to plant roots Phylum Annelida: Annelids are segmented worms
• All annelids (“little rings”) have segmented bodies. • There are about 15,000 species ranging in length from less than 1 mm to 3 m for the giant Australian earthworm. • Annelids live in the sea, most freshwater habitats, and damp soil. Phylum Annelida • protostomes • true coelom • primitive metamerism • all organ systems are present and well developed Properties of Phylum Annelida • Significance of metamerism • Coelomic cavity – reaches a high stage of development in this group of animals • Specialization of the head region into differentiated organs is carried further in some annelids than in other invertebrates considered so far Properties of Phylum Annelida • tendency toward centralization of the nervous system is
more developed: cerebral ganglia (brain), two closely fused ventral nerve cords with giant fibers running the length of the body, and various ganglia with their lateral branches • circulatory system is much more complex than we have seen so far: closed system with muscular blood vessels and aortic arches (“hearts”) for propelling blood Properties of Phylum Annelida • Parapodia: respiratory and locomotor function (introduces
us to the paired appendages and specialized gills found in more highly organized arthropods) • Well developed nephridia in most of the somites: a level of differentiation that involves removal of waste from the blood as well as from the coelom • Annelids are the most highly organized animals capable of complete regeneration (although the ability varies among members of the group) Phylum Annelida is divided into three classes: Oligochaeta, Polychaeta, and Hirudinea Internal anatomy of an earthworm (lateral section): small, long, cylindrical animal without legs or hard body parts. Mouth cavity: entrance to the digestive tract of an earthworm. Pharynx: part of the digestive tract of an earthworm just after its mouth. Ventral nerve cord: set of nerves in the abdomen of an earthworm. Seminal receptacle: pocket related to the semen of an earthworm. Ventral blood vessel: blood vessel situated in the front part of an earthworm. Nephridium: organ of an earthworm that performs the functions of kidneys. Gizzard: pocket used as the stomach of an earthworm. Dorsal blood vessel: blood vessel situated in the rear part of an earthworm. Crop: bulge of the esophagus of an earthworm. Seminal vesicles: small hollow organs that carry the semen of an earthworm. Lateral heart: blood-pumping organ of an earthworm. Esophagus: part of the digestive tract of an earthworm between the pharynx and the crop. Brain: brain of an earthworm. Internal anatomy of an earthworm (cross section): small, long, cylindrical animal without legs or hard body parts. Epidermis: outer part of the skin. Dorsal blood vessel: blood vessel situated in the rear part of an earthworm. Longitudinal muscle: muscular tissue that runs lengthwise on an earthworm. Circular muscle: circular muscular tissue of an earthworm. Intestine: digestive tract of an earthworm. Ventral blood vessel: blood vessel situated in the front part of an earthworm. Body cavity: more or less empty part of an earthworm. Seta: fin thread secreted by an earthworm. Ventral nervous cord: set of nerves in the abdomen of an earthworm. Nephridium: organ of an earthworm that performs the functions of kidneys. General Anatomy The coelom of the earthworm, a typical annelid, is partitioned by septa, but the digestive tract, longitudinal blood vessels, and nerve cords penetrate the septa and run the animal’s Fig. 33.23 DIGESTIVE SYSTEM The digestive system consists of: 1. a pharynx, 2. an esophagus, 3. crop, 4. gizzard, and 5. intestine. Circulatory System Blood with oxygencarrying hemoglobin through dorsal and ventral vessels connected by segmental vessels.
• The dorsal vessel and five pairs of esophageal vessels act as muscular pumps to distribute blood. • Hemoglobin transports 15-20% oxygen used under burrowing conditions. What do they rely on? Excretion In each segment is a pair of excretory tubes, metanephridia, that remove wastes from the blood and coelomic fluid.
• Wastes are discharged through exterior pores. Nervous system A brain-like pair of cerebral ganglia lie above and in front of the pharynx.
• A ring of nerves around the pharynx connects to a sub-pharyngeal ganglion. Reproduction Earthworms are crossfertilizing hermaphrodites.
• Two earthworms exchange sperm and then separate. • The received sperm are stored while a special organ, the clitellum, secretes a mucous cocoon. • As the cocoon slides along the body, it picks up eggs and stored sperm and slides off the body into the soil. Asexual reproduction Some earthworms can also reproduce asexually by fragmentation followed by regeneration. 1 = seminal receptacles (arrow points to two of the four s.r.) 2 = nerve cord (extends length of the animals) 1 = ventral nerve cord 2 = ventral blood vessel 3 = nephridia of three segments 4 = septa 1 = clitellum 2 = dorsal blood vessel 1 = clitellum 2 = genital setae 3 = sperm grroves 4 = sperm ducts 5 = female genital pores 6 = seminal receptacles 1 = intestine 2 = gizzard 3 = crop 4 = six seminal vesicles 5 = seminal receptacles 6 = aortic arches 7 = esophagus 8 = pharynx 9 = suprapharyngeal ganglia 1 = intestine 2 = dorsal blood vessels 3 = cloragogue cells 4 = gizzard 1 = crop 2 = dorsal blood vessel 3 = seminal vesicle 4 = three of the four calciferous glands 5 = fifth pair of aortic arches 6 = seminal receptacle 1 = suprapharyngeal ganglia (“brain”) 2 = pharynx 1 = seminal receptacles (two of the four) 2 = ventral nerve cord Class Polychaeta Polychaete Worm Anatomy • Until this century, leeches were frequently used by physicians for bloodletting.
• Leeches are still used for treating bruised tissues and for stimulating the circulation of blood to fingers or toes that have been sewn back to hands or feet after accidents. Fig. 33.24d • The evolutionary significance of the coelom cannot be overemphasized.
• The coelom provides a hydrostatic skeleton that allows new and diverse modes of locomotion. • It also provides body space for storage and for complex organ development. • The coelom cushions internal structures and separates the action of the body wall muscles from those of the internal organs, such as the digestive muscles. • Segmentation allows a high degree of specialization of body regions.
• Groups of segments are modified for different functions. Phylum Mollusca: Mollusks have a muscular foot, a visceral mass, and a mantle
• The phylum Mollusca includes 150,000 known species of diverse forms, including snails and slugs, oysters and clams, and octopuses and squids. • Most mollusks are marine, though some inhabit fresh water, and some snails and slugs live on land. • Mollusks are soft-bodied animals, but most are protected by a hard shell of calcium carbonate.
• Slugs, squids, and octopuses have reduced or lost their shells completely during their evolution. Despite their apparent differences, all mollusks have a similar body plan with a muscular foot (typically for locomotion), a visceral mass with most of the internal organs, and a mantle.
• The mantle, which secretes the shell, drapes over the visceral mass and creates a water-filled chamber, the mantle cavity, with the gills, anus, and excretory pores. • Many mollusks feed by using a straplike rasping organ, a radula, to scrape up food. Fig. 33.16 Most mollusks have separate sexes, with gonads located in the visceral mass.
• However, many snails are outcrossing hermaphrodites. The life cycle of many marine mollusks includes a ciliated larvae, the trophophore.
• This larva is also found in marine annelids (segmented worms) The basic molluscan body plan has evolved in various ways in the eight classes of the phylum. The four most prominent are the Polyplacophora (chitons), Gastropoda (snails and slugs), Bivalvia (clams, oysters, and other bivalves), and Cephalopoda (squids, octopuses, and nautiluses). • Chitons are marine animals with oval shapes and shells divided into eight dorsal plates. • Chitons use their muscular foot to grip the rocky substrate tightly and to creep slowly over the rock surface. • Chitons are grazers that use their radulas to scrape and ingest algae. Fig. 33.17 • Most of the more than 40,000 species in the Gastropoda are marine, but there are also many freshwater species.
• Garden snails and slugs have adapted to land. • During embryonic development, gastropods undergo torsion in which the visceral mass is rotated up to 180 degrees, such that the anus and mantle cavity are above the head in adults. Fig. 33.18 • Most gastropods are protected by single, spiraled shells into which the animals can retreat if threatened.
• While the shell is typically conical, those of abalones and limpets are somewhat flattened. • Other species have lost their shells entirely and may have chemical defenses against predators. Fig. 33.19 • Many gastropods have distinct heads with eyes at the tips of tentacles. • They move by a rippling motion of their foot. • Most gastropods use their radula to graze on algae or plant material. • Some species are predators.
• In these species, the radula is modified to bore holes in the shells of other organisms or to tear apart tough animal tissues. • In the tropical marine cone snails, teeth on the radula form separate poison darts, which penetrate and stun their prey, including fishes. • Gastropods are among the few invertebrate groups to have successfully populated the land. • In place of the gills found in most aquatic gastropods, the lining of the mantle cavity of terrestrial snails functions as a lung. • The class Bivalvia includes clams, oysters, mussels, and scallops. • Bivalves have shells divided into two halves.
• The two parts are hinged at the mid-dorsal line, and powerful adductor muscles close the shell tightly to protect the animal. • When the shell is open, the bivalve may extend its hatchet-shaped foot for digging or anchoring. Fig. 33.20 • The mantle cavity of a bivalve contains gills that are used for feeding and gas exchange. • Most bivalves are suspension feeders, trapping fine particles in mucus that coats the gills.
• Cilia convey the particles to the mouth. • Water flows into mantle cavity via the incurrent siphon, passes over the gills, and exits via the excurrent siphon.
Fig. 33.21 • Most bivalves live rather sedentary lives.
• Sessile mussels secrete strong threads that tether them to rocks, docks, boats, and the shells of other animals. • Calms can pull themselves into the sand or mud, using the muscular foot as an anchor. • Scallops can swim in short bursts to avoid predators by flapping their shells and jetting water out their mantle cavity. • Cephalopods use rapid movements to dart toward their prey which they capture with several long tentacles.
• Squids and octopuses use beaklike jaws to bite their prey and then inject poison to immobilize the victim. • A mantle covers the visceral mass, but the shell is reduced and internal in squids, missing in many octopuses, and exists externally only in nautiluses. Fig. 33.22 • Fast movements by a squid occur when it contracts its mantle cavity and fires a stream of water through the excurrent siphon.
• By pointing the siphon in different directions, the squid can rapidly move in different directions. • The foot of a cephalopod (“head foot”) has been modified into the muscular siphon and parts of the tentacles and head. • Most squid are less than 75 cm long, but the giant squid, the largest invertebrate, may reach 17 m (including tentacles) and weigh about 2 tons. • Most octopuses live on the seafloor.
• They creep and scurry using their eight arms in search of crabs and other food. • Cephalopods have an active, predaceous lifestyle.
• Unique among mollusks, cephalopods have a closed circulatory system to facilitate the movements of gases, fuels, and wastes through the body. • They have a well-developed nervous system with a complex brain and well-developed sense organs.
• This supports learning and complex behavior. • The mantle cavity of a bivalve contains gills that are used for feeding and gas exchange. • Most bivalves are suspension feeders, trapping fine particles in mucus that coats the gills.
• Cilia convey the particles to the mouth. • Water flows into mantle cavity via the incurrent siphon, passes over the gills, and exits via the excurrent siphon.
Fig. 33.21 1.This is the left valve. 2.Anterior (head) end 3.Posterior (tail) end 4.Dorsal (upper) surface 5. Ventral (lower) surface 6. Umbo (oldest part of the shell) 1. Inner surface of the left valve 2. Posterior adductor muscle 3. Anterior adductor muscle 4. Hinge area of shell 5. Small teeth 6. Posterior shell region 7. Umbo 8. Pallial line 1.Left mantle. 2.Anterior adductor muscle 3. Posterior adductor muscle 4. Pericardial cavity 5. Right mantle 6. Incurrent and Excurrent siphons 1. Foot. 2. Anterior adductor muscle 3. Posterior adductor muscle 4. Visceral mass 5. Siphons 6. Gills 7. Boundary of the mouth 8. Right mantle 9. Pericardial cavity Phylum Arthropoda • 1 million species • Over two-thirds of known animals • Great adaptive diversity: invade every possible habitat • Sometimes regarded as the most successful terrestrial animals Phylum Arthropoda • Bilaterally symmetrical • Triplobastic • Protostomes • Digestive system is complete • Circulatory system is open Phylum Arthropoda • Characterized by the presence of a rigid, chitinous exoskeleton • Internal and external segmentation • Each segment bears jointed appendages: forms and function of appendages varies from one type of arthropod to another Phylum Arthropoda • Classification is rather complex; extant arthropods are divided into several subphyla and many classes • Sometimes the subphyla are listed as distinct phyla in other references Subphylum Chelicerata • Body divided into cephalothorax and abdomen • Antennae are absent • Anterior-most appendages (chelicerae) are modifed as pincers or fangs Class Meristomata • Horseshoe crabs • Cephalothorax convex and horseshoe shaped • Long spine at the posterior end of the abdomen • Compound lateral eyes Class Arachnida • Scorpions, spider, ticks, mites • Cephalothorax with six pairs of appendages • Chelicerae, pedipalps, four pairs of walking legs Subphylum Uniramia • One pair of antennae; appendages uniramous • Three classes: Diplopoda, Chilopoda, Insecta Class Diplopoda • Millipedes • Body subcylindrical • Usually two pairs of legs per body segment Class Chilopoda • Centipedes • Body flattened dorso-ventrally • One pair of legs per body segment Class Insecta • Insects • Body with distinct head, thorax, and abdomen • Usually marked constriction between thorax and abdomen Subphylum Crustacea • Two pairs of antennae • Appendages typically biramous • Three or more pairs of appendages that are modified as mouth parts, including hard mandibles • Walking legs are on the thorax • Abdominal appendages are present (opposed to insects) Class Decapoda • Crayfish, crabs, lobsters, etc. • Exoskeleton of chitin hardened by calcium carbonate • Dorsal cephalothorax covered with carapace Dissection of a Shrimp • Macrobrachium • Freshwater shrimp • Examine the external parts: animal is similar to a crayfish– be sure to look at your atlas! Dissection of a Shrimp: External features • Body is divided into an anterior cephalothorax (fused head and thorax) • Posterior abdomen • Portion of the exoskeleton that covers the cephalothorax laterally and dorsally is called the carapace Dissection of a Shrimp: External features • Anterior pointed extension of the carapace between the eyes is called the rostrum • Medial, pointy plate at the end of the abdomen is called the telson • Telson is flanked by a pair of uropods (the most posterior pair of appendages in these animals) Dissection of a Shrimp: External features • 19 pairs of appendages (start with posterior) • Examine each uropod carefully; consists of two flat paddle shaped projections • Uropod is attached to a cylindrical stalk that is connected to the body at the base of the telson • Biramous (two branched) appendage
• Distal medial branch– endopodite; distal lateral branch or exopodite; proximal stalk or protopodite Dissection of a Shrimp: External features • Swimmerets (pleopods) – 5 pairs attached to the abdomen • Numbered 1 through 5 from anterior to posterior Dissection of a Shrimp: External features • Thorax contains 8 pairs of appendages • All 8 pairs have gills attached to their protopodites • Most posterior of the thoracic appendages (5 pairs) are called walking legs or periopods • Periopod #2: contains only the protopodite and the endopodite of the leg • Claw arises because the last segment of the leg is attached at the base of the second to last segment (NO branching on this leg– called chelate) Dissection of a Shrimp: External features • Anterior most thoracic appendages are called maxillipeds (jaw-legs) because endopodites help to chew food and the exopodites place food in the mouth • 3 pairs of maxillipeds Dissection of a Shrimp: External features • Head of the shrimp has 5 pairs of biramous appendages • 2 pairs of maxilla, 1 pair of mandibles, and 2 pairs of antennae Dissection of a Shrimp: Internal features • Heart – posterior end of the thorax along the medial line • Hemolymph is pumped anteriorly and posteriorly through arteries Dissection of a Shrimp: Internal features • Anterior to the heart are two massives sets of muscles • Anterior-posterior – abdominal retractor muscles • Mandibular muscles – attach to the dorsal side of the carapace Dissection of a Shrimp: Internal features • Stomach - lined with exoskeleton as a series of hard bumps– called the gastric mill • Throughout the thoracic cavity is a digestive gland which absorbs most of the food material • Gland tends to liquefy and spread over the entire animal • Waste is passed through the intestine to the anus (located on the telson) • Excretory glands (green glands) Dissection of a Shrimp: Internal features • Ventral nerve cord – two paired nerve cords that lie close together • Circumesophageal connectives – around the esophagus • Supraesophageal ganglion (“brain”) Phylum Arthropoda Class Insecta In species diversity, insects (class Insecta) outnumber all other forms of life combined. • They live in almost every terrestrial habitat and in fresh water, and flying insects fill the air.
• They are rare, but not absent, from the sea. • The study of insect, entomology is a vast field with many subspecialties, including physiology, ecology, and taxonomy. • Class Insecta is divided into about 26 orders. • Flight is one key to the great success of insects.
• Flying animals can escape many predators, find food and mates, and disperse to new habitats faster than organisms that must crawl on the ground. • Many insects have one or two pairs of wings that emerge from the dorsal side of the thorax.
• Wings are extensions of the cuticle and are not true appendages. Fig. 33.32 • Several hypotheses have been proposed for the evolution of wings.
• In one hypothesis, wings first evolved as extensions of the cuticle that helped the insect absorb heat and were later modified for flight. • A second hypothesis argues that wings allowed animals to glide from vegetation to the ground. • Alternatively, wings may have served as gills in aquatic insects. • Still another hypothesis proposes that insect wings functioned for swimming before they functioned for flight. • Insect wings are also very diverse.
• Dragonflies, among the first insects to fly, have two similar pairs of wings. • The wings of bees and wasps are hooked together and move as a single pair. • Butterfly wings operate similarly because the anterior wings overlap the posterior wings. • In beetles, the posterior wings function in flight, while the anterior wings act as covers that protect the flight wings when the beetle is on the ground or burrowing. • The internal anatomy of an insect includes several complex organ systems.
• In the complete digestive system, there are regionally specialized organs with discrete functions. • Metabolic wastes are removed from the hemolymph by Malpighian tubules, outpockets of the digestive tract. • Respiration is accomplished by a branched, chitin-lined tracheal system that carries O2 from the spiracles directly to the cells. Fig. 33.33 • The insect nervous system consists of a pair of ventral nerve cords with several segmental ganglia.
• The two cords meet in the head, where the ganglia from several anterior segments are fused into a cerebral ganglion (brain). • This structure is close to the antennae, eyes, and other sense organs concentrated on the head. • Metamorphosis is central to insect development.
• In incomplete metamorphosis (seen in grasshoppers and some other orders), the young resemble adults but are smaller and have different body proportions. • Through a series of molts, the young look more and more like adults until it reaches full size. • In complete metamorphosis, larval stages specialized for eating and growing change morphology completely during the pupal stage and emerge as adults. Fig. 33.34 Exoskeleton and Molting
• The epidermis secretes the exoskeleton • Advantages to possessing this structure: provides strong support;
provides rigid levers that muscles can attach to and pull against; offers protection; serves as a barrier to prevent internal tissues from drying out; serves as a barrier to prevent infection • The exoskeleton is composed of the polysaccharide chitin and protein bound together to form a complex glycoprotein • The outer surface of the cuticle is called the epicuticle • The thicker portion is called the procuticle; divided into the exocuticle and the endocuticle • In the exocuticle the glycoprotein chains are cross-linked - the process is called tanning Exoskeleton and Molting cont. • In order to grow the arthropod must shed its exoskeleton, and secrete a new and larger one - molting or ecdysis. Insects
There are two general types of metamorphosis: incomplete and complete
1. Incomplete Metamorphosis Early developmental stages are very similar to the adults Only the wings and the reproductive structures gradually develop The immature stages are called nymphs Thus development is egg----> nymph ----> adult 2. Complete Metamorphosis Each of the developmental stages is structurally and functionally very different • The egg develops into an immature larva that eats voraciously • Larvae then forms a transitional stage called the pupa, that is often contained within a cocoon • Within the pupal exoskeleton a metamorphosis takes place and emerging from the cocoon is a sexually mature adult insect • Reproduction in insects is usually sexual, with separate male and female individuals.
• Coloration, sound, or odor bring together opposite sexes at the appropriate time. • In most species, sperm cells are deposited directly into the female’s vagina at the time of copulation. • In a few species, females pick up a sperm packet deposited by a male. • The females store sperm in the spermatheca, in some cases holding enough sperm from a single mating to last a lifetime. • After mating, females lay their eggs on a food source appropriate for the next generation. • Insects affect the lives of all other terrestrial organisms.
• Insects are important natural and agricultural pollinators. • On the other hand, insects are carriers for many diseases, including malaria and African sleeping sickness. • Insects compete with humans for food, consuming crops intended to feed and clothe human populations. • Billions of dollars each year are spent by farmers on pesticides to minimize their losses to insects. Biology of Ticks
Currently considered to be second only to mosquitoes as vectors of human infectious diseases in the world. Obligate hematophagous arthropods that parasitize every class of vertebrates in almost every region in the world. Two major types: ‘hard ticks’ -- sclerotized dorsal plate ‘soft ticks’ -- flexible cuticle Hard ticks: feed for relatively long periods (several days) remain firmly attached to their host bite is painless each stage feeds once -- may involve different hosts Soft ticks: feed briefly and often -- usually on one species tend to live in dry areas most live in sheltered sites near their hosts First identified as agent responsible for transmitting disease known as Texas cattle fever-- Babesia bigemina. Tick relapsing fever Rocky Mountain spotted fever Tularemia Role of ticks in pathogen transmission: Vectors Reservoir transmitted transstadially (from stage to stage) transmitted transovarially (one generation to the next via female ovaries) Each tick species has optimal environmental conditions for development. This determines the geographical location of the ticks and the risk areas for tickborne diseases. Morphology
• The capitulum bears mouthparts: the hypostome • Mouthparts of the ticks are modified for specialized feeding •Among ticks, the pedipalps grasp skin, while the chelicerae cut through it; the hypostome is thrust into the wound and the teeth anchor the tick • During feeding, the pedipalps either bend outward (soft ticks) as the chelicerae and hypostome penetrate the flesh or remain rigidly and intimately associated with the hypostome (hard ticks) during skin penetration; the pedipalps serve as counter-anchors while the tick is attached to the host Mite capitulum Tick capitulum • Mites and ticks possess 3 pairs of walking legs as larvae and 4 pairs as nymphs and adults Differences between Ticks and Mites
Ticks Large; macroscopic Toothed hypostome Haller’s organ present (on 1st tarsi; olfaction) Mites Smaller; microscopic Hypostome unarmed Haller’s organ absent Ticks • Soft Ticks – flexible, tough, bulbous bodies that obscure the mouthparts and most of the legs
Argas • Hard ticks – which have a dorsal sclerotized plate (=scutum) Amblyoma americanum Hard Tick Life Cycle
• Hard ticks have a more rigid life cycle; they have a single larval and
nymphal stage • Most engorge 3 time during their life; unlike soft ticks, they remain attached to the host and feed and engorge for extended periods of time • Typically a larva attacks one animal, attaches, engorges, leaves the animal, molts to the nymphal stage, attacks a second host, attaches, engorges, leaves that animal, molts to the adult stage, and attacks a third host • Males copulate with females on the 3rd host but do not engorge • Females attach for a few days, engorge and leave the host to lay a single clutch of eggs, after which they die Hard Tick Life Cycle cont. • Most ticks are intermittent ectoparasites of mammals, birds and reptiles; however, they usually demonstrate little host specificity • When seeking a host, hard ticks usually climb on vegetation and adopt a posture known as “questing” • Both sexes of ticks are bloodsuckers, although adult males take little blood • Before or during engorgement, the female hard tick is inseminated by the male; spermatophores are introduced into the vagina by the gnathostoma of the male Questing behavior Soft Tick Life Cycle
• Soft ticks are thought to be a more primitive group: they may
have more than one larval stage and 2 or more nymphal stages • Soft ticks are often nest parasites; they feed quickly and repeatedly on the same animals and usually return to their resting-place between meals Tick-Borne Illnesses and Diseases
Pathogenesis attributable to ticks can be categorized as follows: • Anemia. Blood loss due to heavy infections • Dermatosis. Inflammation and itching from a tick bite; due to tick mouthparts, saliva, and bacterial infections • Paralysis. Due to the release of toxic secretions when persons are bitten at the base of the skull • Otoacariasis. Infestation of the inner ear canal by ticks that causes irritation and sometimes secondary infection • Infections. Ticks transmit viruses, bacteria, rickettsia, protozoa, etc. More on the biology of hard ticks
Life cycle is completed in 2-3 years, but may take 6 months to 6 years. Spend >90% of their life unattached from their host. Most are exophilic: live in open environments, meadows, forests. Seasonally active, seeking their hosts when environmental conditions are most suitable. Highly responsive to stimuli: chemical stimuli humidity aromatic chemicals airborne vibrations and body temperature Host seeking behavior of ticks
Ambush strategy ticks climb up vegetation and wait for passing host front legs are held-out in the same manner as insect antenna Hunter strategy tick attacks host emerge from their habitat and run toward their hosts when the animals appear nearby Some ticks use both strategies! Host seeking behavior of ticks
Third strategy ticks which are endophilic use this strategy ticks remain hidden in hosts’ nests and burrows awaiting the arrival Attachment and feeding
Before feeding, tick may wander around on its host for several hours. It inserts only its hypostome into the skin and various substances produced by the salivary glands enter the host during this penetration. During the first 24-36 hours of attachment, there is little or no injestion of blood, and penetration and attachment are the primary activity. The salivary secretions include: 1. cement to anchor the mouthparts to the skin of the host. 2. Anti-inflammatory substances 3. Anti-hemostatics and immunosuppressives Attachment and feeding II
Hard ticks feed for long periods of time (2-15 days required for complete blood meal to be digested. Initial feeding: slow-feeding period (3-4 days) Rapid engorgement (1 - 3 days) females can increase body weight up to 120X While feeding, there are alternating periods of sucking blood and salivation. Regurgitation occurs frequently, particularly at the end of the engorgement phase. Attachment and feeding III
During initial, slow feeding, there is continuous digestion of blood meal in the midgut, and defecation occurs. During rapid engorgement, there is reduced digestion. Resumes once detached from the host. Rapid concentration of the blood meal by eliminating water and electrolytes in the feces, during transpiration, and in salivary gland secretions. Soft ticks
Several different properties from hard ticks. Salivary glands do not produce cement and contain anticoagulant and cytolytic substances, because feeding only takes a brief time. Soft ticks may feed up to 10 times for only several hours ! After blood meals, these ticks are often found in the cracks in their habitats or just below the soil surface. Tick paralysis
Prolonged attachment (5-7 days) of certain species of ticks may result in paralysis of the host. Neurotoxic substances produced by the salivary glands of attached engorged ticks (particularly female ticks). Occurs more often in children. Symptoms: weakness in lower extremities trunk musculature upper extremities head Removal of the tick leads to rapid recovery within 24 hours! Tick control
Reducing and controlling tick populations have been difficult. Habitat modifications: vegetation management by cutting, burning, and herbicide treatment drainage of wet areas modifications are usually short-lived, and ecological changes can be severe ! Organic phosphates combined with pheromones have been used, but these regimens have toxic effects on animals and humans. Tick control II
Biological control methods: promotion of natural predators beetles, spiders, ants parasites nematodes bacterial pathogens release of sterile males Immunization of hosts against ticks. How to treat tick bites
Removing ticks from the skin: Rounded forceps and a magnifying glass should be used! Grasp mouthparts of the tick as close as possible to the skin. Pull tick upward, perpendicular to the skin with steady and continuous action. Usually any mouthparts of the ticks retained in the skin are eliminated uneventfully by the body. Disinfectant should be applied and the tick stored at -20 C in case patient later develops infection. Biology of Mosquitoes Biology of Mosquitoes
*Life cycle of mosquitoes. *Development of pathogens, both viral and parasitic, in mosquitoes. *Insect immunity: insect response to the pathogen. Genetic basis of vector competence. Generation of genetically-altered mosquitoes. Wuchereria bancrofti
• This filarial worm is parasitic only to humans
• It is characterized by extensive enlargement of extremities • Ancients likened the thickened skin to that of elephants, hence the misnomer elephantiasis (which literally means “caused by elephants” rather than “like elephants”) Patient with river blindness Patient suffering from severe dermatitis Basic facts about mosquitoes and the diseases they transmit.
Mosquitoes are by far the most medically important arthropod vector of disease. Malaria Lymphatic filariasis Viral diseases Mosquitoes and the diseases they transmit still plague people all over the world, especially in tropical and third-world countries. Despite all of the effort to control mosquitoes and malaria transmission, the public health issues associated with this arthropod are even worse today than 30 years ago. 1. Mosquitoes are responsible for more human death than any other living organism. 2. Male mosquitoes do not bite. The risk is from female mosquitoes which bite when in search of a blood meal to provide protein for their eggs. 3. Most adult mosquitoes live for about two weeks. 4. There are over 2,500 species of mosquitoes in the world. 5. The swelling that appears after a mosquito leaves isn’t from the bite - it's an allergic reaction to saliva the mosquito injected under the skin to prevent the blood from clotting 6. Mosquitoes like dark areas and can suck the juice out of plants in order to live - including tree leaves, grass, shrubs, etc. 7. Mosquito larvae develop in standing water, mud, ponds, tin cans, under decks, puddles and old tires, etc. 8. Mosquitoes rarely travel farther than 300 feet from their birthplace. 9. Studies have shown that while bats devour a huge number of insects, mosquitoes are only a small part of their diet. 10. Mosquitoes are found all over the world, even in the Arctic General Life Cycle of Mosquitoes These images of the mosquito show in fascinating detail the body parts of this common arthropod. At the left, you can see its large compound eyes. Despite their size, the mosquito doesn't find its victim by sight ... rather, it uses chemical sensors to detect carbon dioxide given off by its prey. The mosquito at the right is just emerging from its pupa stage under the surface of a pond. Only female mosquitoes draw blood; they need it to provide nourishment for their eggs. What you see on the left is a scanning electron microscope view of the tip of a mosquito's proboscis. The actual tube that punctures skin is like a hypodermic needle and is hidden inside. As the 'needle' (stylet) emerges from its sheath and enters skin, the mosquito first injects anti-coagulant into the blood, to thin it and keep it from coagulating in its stomach. It is this anticoagulant that causes the allergic reaction in skin, resulting in redness and itching. Some mosquito breeding grounds General Anatomy of Mosquito Larvae More mosquito breeding grounds Distinguishing head structures among different mosquitoes Some Abdominal Differences Pathogen development in mosquitoes
Major routes of migration and developmental sites for three major pathogen groups: (viruses, malaria parasites, filarial worms) 1. All pathogens transmitted by mosquitoes are acquired with a blood meal. 2. Pathogen enters the midgut. There are different pathways for the different groups of pathogens. Development of viruses in mosquitoes
Enter the midgut epithelial cells. Replicate Exit the cells Travel through the hemolymph-filled hemocoel to the salivary glands. Replicate again and reside until injected into vertebrate host. Development of malaria parasites in mosquitoes
Bloodmeal is acquired. Enter the midgut. Migrate through the peritrophic matrix. Enters the midgut epithelial cells. Maturation. Travel through the hemocoel, and invade salivary glands. Injection into next vertebrate host. Development of filarial worms in mosquitoes
Human filarial worms: Enters the midgut. Penetrate the midgut epithelium, migrate to the thoracic musculature. Infective larvae break out of thoracic musculature and travel through the hemocoele, migrating to the head. Worms actively emerge from the head of the mosquito. Dog heartworm Similar to human filarial worms, but travel to the Malpighian tubules instead, develop intracellularly, emerge, travel to the head, and worms emerge from the head of the mosquito during feeding. Mosquito-pathogen interactions: salivary glands
Salivary glands synthesize and secrete powerful anti-hemostatic agents that facilitate blood feeding. Mosquito-pathogen interactions: midgut
Hostile environment for a pathogen: why? temperature change pH changes abruptly proteolytic enzymes begin digestion ingested blood may lose its liquid nature formation of a peritrophic matrix around blood meal Exiting the midgut is a necessary strategy for mosquitoborne diseases. filarial worms (nematodes) leave quickly malaria parasites use the blood meal for sexual reproduction Mosquito-pathogen interactions: midgut
Shortly after a blood meal is ingested, midgut cells secrete a peritrophic matrix composed of proteins embedded within chitin. It has been suggested that the peritrophic matrix protects the mosquito from pathogens, keeps protease inhibitors within the lumen, and functions as a solid support and a filter. Complete formation of the peritrophic matrix takes 12-30 hours. Does not serve as a barrier for filarial worms or viruses which penetrate within several hours. Traversing the peritrophic matrix by malaria parasites
P.gallinaceum produces a chitinase enzyme that enables the ookinete to penetrate this barrier. The parasite also relies on the mosquito’s trypsin enzymes to activate the parasite enzymes. P.falciparum also produces a chitinase; P.vivax crosses the peritrophic matrix before it is completely synthesized, eliminating the need for the chitinase. Traversing the peritrophic matrix by other pathogens
Our understanding of this process by other pathogens is not well established. Filarial worms traverse the peritrophic matrix via the use of a cephalic hook that enables them to migrate out of the midgut. Mosquito-borne viruses may use a recetor-ligand interaction: how would you demonstrate whether this was the case? Inside midgut epithelial cells
Once malaria parasites traverse the blood meal and the peritrophic matrix, they are not home-free -- and are still susceptible to destruction by a process called encapsulation. Encapsulation is a primitive mechanism of immunity used by arthropods to destroy pathogens. Encapsulation explains the refractoriness of certain mosquito species to certain parasites. For example, the avian malaria P.gallinaceum cannot develop in the mosquito vector of human malaria, Anopheles gambiae. Hemocoele
Review: within the hemocoele, tissues and organs are bathed in hemolymph, the medium that transports nutrients and other substances throughout the mosquito. Immune system molecules in mosquitoes are both discriminatory and efficient. Although there is no antibody and immune system memory responses as seen in vertebrate immune responses, there is a set of humoral and cellular weapons. Mosquito-pathogen interactions: some things to consider
Behavioral and environmental factors play a role in determining the vector capacity. For example: A particular mosquito species may be genetically and biochemically compatible for the complete development of a particular pathogen, but if the mosquito does not co-exist with the vertebrate host, this mosquito is not a suitable host for this pathogen. If the blood source for this particular pathogen is not present, then this mosquito is not an appropriate vector for this pathogen. Food for thought: Which avenue should we study in mosquito-pathogen interactions? Resistance or susceptibility to pathogens?
1. How do pathogen-resistant mosquitoes kill invading microorganisms? 2. How do susceptible mosquitoes co-exist with the pathogen? Much more effort has been placed on the first perspective. **Understanding the immune system of mosquitoes. Red Imported Fire Ant Solenopsis invicta Polymorphic workers Queen Accidentally introduced in the 1930s Recently found in Australia The problem with imported fire ants is that there are so many of them. 4-8 Tons of Fire Ants per Square Mile Major Types of Problems
1. Agricultural 2. Electrical 3. Medical 4. Ecological Agricultural Electrical Medical Ecological Problems • Phorid Decapitating Flies • Fire Ant Pathogens • Black-capped Vireo Conservation • Areawide Demonstration Projects Phorid Decapitating Flies At least 20 species of phorids attack fire ants in South America Collection & Exportation Rearing & Testing in Quarantine Permits Mass Rearing Field Release Bed Bugs : Bed Bugs Basic Biology and Control
Adapted from http://www.utoronto.ca/forest/termite/Bedbugs Taxonomic Hierarchy
Scientific Name: Cimex lectularius Common Name: the Common Bed Bug Adult Female Adult Male Description
Small – 3/16 inch long, oval, flat, reddish brown insects Vestigial wings & a thin coat of fine golden hairs Give off a distinctive “musty, sweetish” odor Undigested blood in feces causes “rusty” spots Males – pointed abdomen Females – rounded abdomen Biology
Feed only on Blood – Mammals or Birds Attach small (1 mm) whitish eggs to surfaces in harborages where they hide in loose clusters 5 Nymphal instars ( Need >1 blood meal each instar ) Life Cycle takes 4-5 weeks (egg-to-egg) in ‘good’ conditions [ 7580% RH; 83-90 degrees F ] Female may lay 200-500 eggs in her lifetime Adults can survive >1 yr. w/o feeding [ Nymphs 3-4 mo.] Feeding - Several Instars Eggs and Droppings ‘Spots’ on Bedding Rusty Spots Medical Importance
- Found naturally infected w/ >20 human pathogens - Never proven to transmit any human disease - Several species feed on humans (including: Common & Tropical Bed Bugs, Bat Bugs, & Poultry Bugs - Salivary proteins cause “sensitivity” to repeated bites by large numbers of bed bugs
- - 5 stages: no reaction; delayed reaction; both immediate & delayed; immediate reaction only; & finally, no reaction - - True hypersensitivity can develop (but it is reversible) - Serious social stigma to “having” an infestation Typical Feeding Postures Feeding a “Colony” Immediate Bite Reactions Delayed Reactions (> 24 hrs.) Habits ( Behavior )
- Nocturnal, harbor in clusters, but NOT ‘social’ - Hide in daytime in cracks, crevices, behind baseboards, bed frames, mattress seams, etc. - Take a blood meal to repletion in 3-10 min. - “Prefer” humans but feed on other hosts, too - Travel 15-20 ft. (each way) nightly to feed - Feed every few days if hosts available - Often void part of previous meal while feeding - Can remain fully active at 45o F [ if acclimated for 24 hrs at < 60o F ] Bugs Have Thin Flat Bodies Survey Sites: Bed Frames Mattress (especially Seams) Upholstered Chairs Window Curtains & Frames Control Strategies
- Thorough survey & accurate ID - Educate customers ( may take > 1 visit ) - Sanitation will NOT eliminate them - Initial vacuuming (mattresses, beds, harborages ) - Treat harborages w/ properly labeled residual - - try to not use highly repellent materials - Dust electrical boxes, voids (maybe seal them shut ) - Seal harborages shut (pref. silicone-based sealant ) - Consider physical barriers if appropriate - Sticky monitors ( may detect continued presence) “New” Techniques & Products 1. Gentrol™ labeled for Bed Bugs (late-2003) 2. Heat Treatments ( Whole-House or Room) 3. Steaming – Matresses, or Beds, etc. 4. Phantom™ (Chlorfenapyr) labeled to control ants / roaches; indoor ‘crack-and-crevice’ 5. PCO Pellets™ (Acephate) still labeled for ‘crack-and-crevice’ treatments 6. Encase matress & Pillows in plastic covers 7. Permethrin repellent, over-the-counter (s-h) Fumigation Fumigation
1. “Whole structure” fumigation will eliminate bugs present within treated areas, but . . . . .
a. This is seldom economically practical. b. There is no residual protection. 2. The same things are true for . . .
a. “Batch” or “Single-Room” Fumigations, b. Heat treatments (Whole Bldg. or One - Room), and c. Cold treatments (Whole Bldg. or One - Room). Monitors May Help Detect Bed Bugs Why Bed Bugs Are Increasing
1. Greater human mobility 2. Less use of any residuals – last 5-6 yrs 3. Significant switch to baits for roaches & ants 4. Many professionals are not familiar w/ bed bugs
- inadequate survey, wrong ID, incomplete treatment 5. Pyrethroids used in most accounts are repellent
- bugs do not get a lethal dose (esp. in deep cracks) - harborages easy to miss in first survey - bugs may detect & avoid residual treatments - bug pop. often “split” or move from such treatments 6. People may call any unknown bite - “bed bugs” Cockroaches Cockroaches
•And Disease Basics
• 4000 species worldwide • 57 species in the U.S. • 18 species have become serious domestic pests • The most important medically are:
• Blattella germanica (German cockroach) • Blatta orientalis (Oriental cockroach) • Periplanta americana (American cockroach) • Supella longipalpa (Brown-banded cockroach) Biology
• Like warmth (climate plays a role)
• Cold Climates • Warm Climates • Nocturnal • Omnivorous • Live for 5-10 weeks without water • Live many months without food
• Not a limiting factor • Nymphs often die 7-10 days Life Cycle • Eggs are laid encased in a capsule called an ootheca
• Typically 18-40 • Deposited or cemented to surfaces • 4-90 ootheca • Nymphs
• Hatch after 1-3 months • Wingless • Number of nymphal stages and length varies with species. • “Medical” Importance
• (1) Get into our food supplies • (2) Odor (Some stink!) • (3) They feed on humans • (4) Allergies • (5)Transmit pathogens? • We tend to call cockroaches insects of sanitary importance. American Cockroach
Periplaneta americana • Originally from Africa. • Like damp environments. • Sewers, around pipes, ships. • Basement or first floor in buildings. • Nymphal stage 10-14 months long. German Cockroach
• Most common species in WY. • Originally from Africa. • Smaller than American. • Basement and first floors in buildings. • Carries egg capsule. • Nymphal stage 2-3 Oriental Cockroach
• Shiny black, common in WY. • Found in sewers, likes basement. • More tolerant of cooler temps. • Males have short wings, females are long. • Nymphal stage 12-15 months long. Brown-Banded Cockroach
• Originally from Cuba. • 2 broad dorsal bands. • All rooms in house. • Likes high places versus low. • Big problem in the Southern U.S. • Glue eggs to things. Control
• Be clean! • Insecticidal spraying
• E.g. malathion, carbamates • Pyrethroids
• E.g. permethrin • Boric Acid Powder (borax)
• Contact insecticide and stomach poison. • Organophosphates and Carbamate Insecticides
• 1-2% added to baits of food • Insect Growth Regulators (IGRs)
• E.g fenoxycarb, hydrophen, methoprene. What Makes the Cockroach a Good Model System? • A large number of cockroaches are easy to raise and be maintained in laboratories. • Cockroaches can be stored at 15˚C for very extended periods of time. • Cockroaches are conveniently available in several different sizes. (c) http://pested.unl.edu/comproa.jpg • The cost of raising cockroaches can vary. • The smaller the cockroach, the shorter the life cycle. • Cockroaches can be extremely genetically manipulated • Very few species of cockroach have any economic importance. • Those who show an interest in the cockroach include the following: ~ pesticide industries ~ medical communities ~ neurobiologists ~ developmental biologists • Finally, the ability of several laboratory species of cockroaches to be cultured and tested provides us with a perfect animal for numerous studies.
©Iziko Museums of Cape Town ©Iziko Museums of Cape Town Research in Genetics
• Cockroach Biology • Cytogenetics • Behavior • Insecticide Resistance Research in Neurobiology
• Escape Behaviors • Sensory Input Reactions • Brain Centers and Evolution Research in Development
• Embryonic Development and Life Cycles • Development and the availability of food • Social Environment Development Family Reduviidae
(Assassin bugs, Kissing bugs) • Sub-family: Triatominae • More than 130 species in 16 genera. • Evolved into a blood feeder that feeds on a wide variety of hosts. • Why called kissing bug? Chagas Disease
• Host: Variety of vertebrates. • Vector: Triatoma spp.
• Triatoma infestans • Triatoma dimidiata • Triatoma brasiliensis • Rhodnius prolixus • Panstrongylus megistus • Etiologic Agent: Trypanosoma cruzi (protozoan) • Reservoir: Wild animals (opossums, armadillos, rodents, monkeys, etc). Distribution
• Most Triatoma occur in the Americas. • From the Great Lakes of the U.S. to Southern Argentina. • 13 species are found in the Old World tropics. • All medically important species are confined to the Southern U.S., Central and South America. Life Cycle of the Vector
• Egg Nymph Adult (6-10 months • Eggs
• Deposited in or near the habitation of host. • Nymph
• Hatch after 10-15 days • Stay hidden for 2-3 days • 5 instars (each requires 1 blood-meal) • Can ingest 6-12 times their weight in blood. • wingless • Adult
• 1-2 eggs laid each day; 200-300 over lifetime Life Cycle Transmission
People can become infected with T. cruzi by: • unknowingly touching their eyes, mouth, or open cuts after having come into contact with infective triatome bug feces • bugs directly depositing infected feces in their eyes • eating uncooked food contaminated with triatome bug feces • receiving infection from mother during pregnancy or at birth • receiving an infected blood transfusion or organ transplant • Animals can become infected in the same way, or they might eat an infected bug. Medical Importance
• Affects an estimated 16-18 million people throughout South and Central America and Mexico. • 50,000 die each year! • In the United States only 5 cases have been reported in humans. • Domestic transmission cycle, Southern Texas USA. Case Study: San Benito, Texas
• Three pet dogs died from Chagas cardiomyopathy. • Blood drawn from dogs and owners. • A follow-up serologic survey was conducted. • Inspection of the residence. • Triatoma gerstaeckeri • Domestic transmission cycle. Signs and Symptoms
• There are three stages of infection in Chagas disease. • (1) Acute Stage – 1% of cases • Romaña's sign – a person's eye on one side of the face swells, usually at the bite wound or where feces were deposited or accidentally rubbed into the eye. • fatigue, fever, enlarged liver or spleen, swollen lymph glands Signs and Symptoms
• (2) Indeterminate Stage
• 8-10 weeks after infection • Once it begins it may last many years • people do not have symptoms. • (3) Chronic Stage
• 10-40 years after infection 20-30% of infected people may develop the most serious symptoms of Chagas disease. • Cardiac problems, including an enlarged heart; altered heart rate or rhythm; heart failure; or cardiac arrest. • enlargement of the esophagus or large bowel, which results in problems with swallowing or severe constipation. Prevention and Control
• Avoid sleeping in thatch, mud, or adobe houses. • Use insecticides
• In some countries, the blood supply may not always be screened for Chagas disease. • Bed Net with insecticides. • Camp under cover. Prevention and Control
• Control is based on spraying residual insecticides inside houses on walls, floors and roofs. • Insecticidal Smoke Bombs • Make the houses unattractive resting sites for bugs.
• Plaster walls to cover up cracks. • Cost is high for re-housing. Introduction to Deuterostomes
• At first glance, sea stars and other echinoderms would seem to have little in common with the phylum Chordata, which includes the vertebrates. • However, these animals share the deuterostome characteristics of radial cleavage, development of the coelom from the archenteron, and the formation of the anus from the blastopore. • These developmental features that define the Deuterostomia are supported by molecular systematics. Fig. 32.7 Phylum Echinodermata: Echinoderms have a water-vascular system and secondary radial symmetry
• Sea stars and most other echinoderms are sessile, or slow-moving animals. • The internal and external parts of the animal radiate from the center, often as five spokes. • A thin skin covers an endoskeleton of hard calcareous ossicles, pedicellariae, and dermal branchiae.
• Most echinoderms are prickly from skeletal bumps and spines that have various functions. • Unique to echinoderms is the water vascular system, a network of hydraulic canals branching into extensions called tube feet.
• These function in locomotion, feeding, and gas exchange. • Sexual reproduction in echinoderms usually involves the release of gametes by separate males and females into the seawater.
• The radial adults develop by metamorphosis from bilateral larvae. • The radial appearance of most adult echinoderms is the result of a secondary adaptation to a sessile lifestyle.
• Their larvae are clearly bilateral and even echinoderm adults are not truly radial in their anatomy. • All 7,000 or so species of echinoderms are marine. They are divided into six classes (4 of them studied in the lab):
• Asteroidea (sea stars) • Ophiuroidea (brittle stars) • Echinoidea (sea urchins and sand dollars) • Holothuroidea (sea cucumbers) • Sea stars (class Asteroidea) have five arms (sometimes more) radiating from a central disk. • Beneath the epidermis of sea stars is a mesodermal endoskeleton of small calcareous plates, or ossicles, bound together with connective tissue. Fig. 33.38 • From the ossicles project the spines and tubercles that are responsible for the spiny surface. Fig. 33.38 • The undersides of the arms have rows of tube feet.
• Each can act like a suction disk that is controlled by hydraulic and muscular action. • They project from ambulacral grooves. • Viewed from the oral side, the large radial nerve can be seen in the center of each ambulacral groove. Along the edges of the ambulacral groove one can see ambulacral spines. • The water vascular system is another coelomic compartment and is unique to echinoderms. • It is a system of canals and specialized tube feet • In sea stars, the primary function of the water-vascular system are locomotion and food gathering, as well as respiration and excretion. Fig. 33.38 • Locomotion by means of tube feet illustrates the interesting exploitation of hydraulic mechanisms by echinoderms. The valves in the lateral canals prevent backflow of fluid into the radial canals. Tube foot has in its walls connective tissue that maintains the cylinder at a constant diameter. • • Feeding and Digestion
Mouth leads to two-part stomach: cardiac stomach and pyloric stomach. Many sea stars are carnivorous– they can feed on molluscs, crustaceans, polychaetes, other echinoderms, and sometimes small fish. Many show particular preferences. Some will feed on brittle stars, sea urchins, or sand dollars, swallowing them whole and later regurgitating undigestible ossicles and spines. • Sea stars use the tube feet to grasp the substrate, to creep slowly over the surface, or to capture prey. Asterias is a significant predator of commercially important clams and oysters.
• When feeding on closed bivalves, the sea star grasps the bivalve tightly (can be up to 1300 g). • In half an hour or so, the adductor muscles of the clam are fatigued, and relax. The sea star everts its stomach through its mouth and into the narrow opening between the shells of the bivalve. • Enzymes from the sea star’s digestive organs then begin to digest the soft body of the bivalve inside its own shell. • Hemal system: function unclear– has nothing to do with circulation Sensory and nervous system: nervous system is composed of three subsystems
1. Nerve ring 2. Radial nerves 3. Nerve net connects the system. 4. Sensory cells scattered over the epidermis. • • Reproductive system: most stars have separate sexes. Gonads are in each interradial space, and fertilization is external. Sea stars can regenerate lost parts. Stars also have the power of autonomy (the ability to break off their own bodies). An arm make take months to regenerate. If an arm is broken off or removed, and it contains part of the central disk, the arm can regenerate a complete new sea star!! • • • Sea stars and some other echinoderms can regenerate lost arms and, in a few cases, even regrow an entire body from a single arm. Fig. 33.37a • • Development of sea stars: early embryogenesis shows the typical deuterostome pattern. Gastrulation is by invagination. Anterior end of the archenteron pinches off to become the coelomic cavity. Metamorphosis involves a dramatic reorganization of a bilateral larva into a radial juvenile!! What was on the left side becomes the oral surface, and the larval right side becomes the aboral surface. • • http://www.pgjr.alpine.k12.ut.us/ science/whitaker/Animal_Kingdo m/SeaStar/SeaStar.html
•http://faculty.orangecoastcollege.edu /mperkins/zoo-review/seastar/index.html 2. Phylum Chordata: The chordates include two invertebrate subphyla and all vertebrates
• The phylum to which we belong consists of two subphyla of invertebrate animals plus the subphylum Vertebrata, the animals with backbones. • Both groups of deuterostomes, the echinoderms and chordates, have existed as distinct phyla for at least half a billion years, but they still share similarities in early embryonic development. Introduction to Vertebrates
• Humans and their closest relatives are vertebrates.
• This group includes other mammals, birds, lizards, snakes, turtles, amphibians, and the various classes of fishes. • They share several unique features including a backbone, a series of vertebrae. • The vertebrates belong to one of the two major phyla in the Deuterostomia, the chordates. • The phylum Chordata includes three subphyla, the vertebrates and two phyla of invertebrates, the urochordates and the cephalochordates. Fig. 34.1 1. Four anatomical features characterize the phylum Chordata
• Although chordates vary widely in appearance, all share the presence of four anatomical structures at some point in their lifetime.
• These chordate characteristics are a notochord; a dorsal, hollow nerve cord; pharyngeal slits; and a muscular, postanal tail.
Fig. 34.2 1. The notochord, present in all chordate embryos, is a longitudinal, flexible rod located between the digestive tube and the nerve cord.
• It is composed of large, fluid-filled cells encased in fairly stiff, fibrous tissue. • It provides skeletal support throughout most of the length of the animal. • While the notochord persists in the adult stage of some invertebrate chordates and primitive vertebrates, it remains as only a remnant in vertebrates with a more complex, jointed skeleton. • For example, it is the gelatinous material of the disks between vertebrae in humans. 2. The dorsal, hollow nerve cord develops in the vertebrate embryo from a plate of ectoderm that rolls into a tube dorsal to the notochord.
• Other animal phyla have solid nerve cord, usually located ventrally. • The nerve cord of the chordate embryo develops into the central nervous system: the brain and spinal cord. 3. Pharyngeal gill slits connect the pharynx, just posterior to the mouth, to the outside of the animal.
• These slits allow water that enters the mouth to exit without continuing through the entire digestive tract. • In many invertebrate chordates, the pharyngeal gill slits function as suspension-feeding devices. • The slits and the structures that support them have become modified for gas exchange (in aquatic vertebrates), jaw support, hearing, and other functions during vertebrate evolution. 4. Most chordates have a muscular tail extending posterior to the anus.
• In contrast, nonchordates have a digestive tract that extends nearly the whole length of the body. • The chordate tail contains skeletal elements and muscles. • It provides much of the propulsive force in many aquatic species. 2. Invertebrate chordates provide clues to the origin of vertebrates
• Most urochordates (Subphylum Urochordata), commonly called tunicates, are sessile marine animals that adhere to rocks, docks, and boats.
• Others are planktonic. • Some species are colonial, others solitary. • Tunicates are suspension-feeders.
• Seawater passes inside the animal via an incurrent siphon, through the pharyngeal gill slits, and into a ciliated chamber, the atrium. • Food filtered from the water is trapped by a mucous net that is passed by cilia into the intestine. • Filtered water and feces exit through an excurrent siphon. • The entire animal is encased in a tunic of a celluloselike carbohydrate. Fig. 34.3a, b • While the pharyngeal slits of the adult are the only link to the chordate characteristics, all four chordate trademarks are present in the larval forms of some tunicate groups.
• The larva swims until it attaches its head to a surface and undergoes metamorphosis, during which most of its chordate characteristics disappear. Fig. 34.3c • Cephalochordates (Subphylum Cephalochordata), also known as lancelets, closely resemble the idealized chordate.
• The notochord, dorsal nerve cord, numerous gill slits, and postanal tail all persist in the adult stage. • Lancets are just a few centimeters long. • They live with their posterior end buried in the sand and the anterior end exposed for feeding. (a) Fig. 34.4 (b) • Lancelets are suspension feeders, feeding by trapping tiny particles on mucus nets secreted across the pharyngeal slits.
• Ciliary pumping creates a flow of water with suspended food particles into the mouth and out the gill slits. • In lancets, the pharynx and gill slits are feeding structures and play only a minor role in respiration, which primarily occurs across the external body surface. • A lancet frequently leaves its burrow to swim to a new location. • Though feeble swimmers, their swimming mechanism resembles that of fishes through the coordinated contraction of serial muscle blocks.
• Contraction of these muscles flexes the notochord and produces lateral undulations that thrust the body forward. • The muscle segments develop from blocks of mesoderm, called somites, arranged serially along each side of the notochord of the embryo. • Molecular evidence suggests that the vertebrates’ closest relatives are the cephalochordates, and the urochordates are their next closest relatives. • The evolution of vertebrates from invertebrates may have occurred in two stages.
• In the first stage, an ancestral cephalochordate evolved from an organism that would resemble a modern urochordate larva. • In the second, a vertebrate evolved from a cephalochordate. • This first stage may have occurred through paedogenesis, the precocious development of sexual maturity in a larva.
• Changes in the timing of expression of genes controlling maturation of gonads may have led to a swimming larva with mature gonads before the onset of metamorphosis. • If reproducing larvae were very successful, natural selection may have reinforced paedogenesis and eliminated metamorphosis. • The paedogenetic hypothesis is deduced from comparing modern forms, but no fossil evidence supports or contradicts this hypothesis. • Several recent fossil finds in China provide support for the second stage, from cephalochordate to vertebrate.
• They appear to be “missing links” between groups. • Features that appear in these fossils include a more elaborate brain, eyes, a cranium, and hardened structures (“denticles”) in the pharynx that may have functioned somewhat like teeth. Fig. 34.5 1. Neural crest, pronounced cephalization, a vertebral column, and a closed circulatory system characterize the subphylum Vertebrata
• The dorsal, hollow nerve cord develops when the edges of an ectodermal plate on the embryo’s surface roll together to form the neural tube. • In vertebrates, a group of embryonic cells, called the neural crest, forms near the dorsal margins of the closing neural tube. • Neural crest contributes to the formation of certain skeletal elements, such as some of the bones and cartilages of the cranium, and other structures.
• The vertebrate cranium and brain (the enlarged anterior end of the dorsal, hollow nerve cord) and the anterior sensory organs are evidence for a high degree of cephalization, concentration of sensory and neural equipment in the head. Fig. 34.6 • Organisms that have the neural crest and a cranium are part of the Subphylum Craniata which includes the vertebrates and the hagfishes.
• Hagfishes lack vertebrae but do have a cranium. • The cranium and vertebral column are parts of the vertebrate axial skeleton.
• This provides the main support structure for the central trunk of the body and makes large body size and fast movements possible. • Also included in the axial skeleton are ribs, which anchor muscles and protect internal organs. • Most vertebrates also have an appendicular skeleton, supporting two pairs of appendages (fins, legs, or arms). • The vertebrate endoskeleton is made of bone, cartilage, or some combination of the two materials.
• Although the skeleton is a nonliving extracellular matrix, living cells within the skeleton secrete and maintain the matrix. • The vertebrate endoskeleton can grow continuously, unlike the exoskeleton of arthropods. • Active movement by vertebrates is supported by ATP generated through aerobic respiration.
• These movements may be to acquire prey or to escape predators. • Adaptations to the respiratory and circulatory systems support mitochondria in muscle cells and other active tissues. • These include a closed circulatory system, with a ventral, chambered heart that pumps blood through arteries and capillaries to provide nutrients and oxygen to every tissue in the body. • The blood is oxygenated as it passes through capillaries in gills or lungs. • An active lifestyle requires a large supply of organic fuel.
• Vertebrate adaptations for feeding, digestion, and nutrient absorption help support active behavior. • These multiple adaptations in form and function to a variety of systems have supported the transition from a relatively sedentary lifestyle in prevertebrates to a more active one pursued by most vertebrates. Brief overview of vertebrate diversity
• Our current understanding of vertebrate phylogeny is based on anatomical, molecular, and fossil evidence.
• At the base are hagfishes and lampreys which lack hinged jaws. • All other vertebrates, the gnathostomes, have true jaws and also two sets of paired appendages. • In “fishes,” including the cartilaginous fishes and three classes of bony fish, these paired appendages function in swimming. • In tetrapods, the appendages are modified as legs to support movements on land. • Among tetrapods, most amphibians lay eggs in water or an otherwise moist environment. • The other terrestrial tetrapods are amniotes, producing shelled, water-retaining eggs which allow these organisms to complete their life cycles entirely on land. • While most modern mammals do not lay eggs, they retain many of other key features of the amniotic mode of reproduction. • The traditional vertebrate group known as “reptiles” (turtles, snakes, lizards, crocodiles, and alligators) does not form a monophyletic group unless birds are included. Fig. 34.7 Introduction to Jawless Vertebrates
• The two extant classes of jawless vertebrates, the Superclass Agnatha, are the hagfishes and the lampreys.
• These are eel-like in shape, but the true eels are bony fish. • The agnathans are an ancient vertebrate lineage that predates the origin of paired fins, teeth, and bones hardened by mineralization (ossification). Class Myxini: Hagfishes are the most primitive living “vertebrates”
• All of the 30 or so species of hagfishes are marine scavengers, feeding on worms and sick or dead fish.
• Rows of slime glands along a hagfish’s body produce small amounts of slime to perhaps repulse other scavengers or larger amounts to deter a potential predator. Fig. 34.8 • The skeleton of hagfish is made entirely of cartilage, a rubbery connective tissue.
• In addition to a cartilaginous cranium, the hagfish notochord is also cartilaginous, providing support and a skeleton against which muscles can exert force during swimming. • Hagfishes lack vertebrae.
• Therefore, they belong more precisely in the larger group of chordates, the Craniata, and are equated with the Vertebrata. • Hagfishes diverged from ancestors that produced the vertebrate lineage about 530 million years ago. Class Cephalaspidomorphi: Lampreys provide clues to the evolution of the vertebral column
• There are about 35 species of lampreys inhabiting both marine and freshwater environments.
• The sea lamprey is an ectoparasite, that uses a rasping tongue to penetrate the skin of its fish prey and to ingest the prey’s blood and other tissues. Fig. 34.9 • Sea lampreys live as suspension-feeding larvae for years in streams before migrating to the sea or lakes as predaceous/parasitic adults.
• These larvae resemble the lancelets. • Some species of lampreys feed only as larvae.
• After metamorphosis, they attain sexual maturity, reproduce, and die within a few days. • The notochord persists as the main axial skeleton in adult lampreys.
• Lampreys also have a cartilaginous pipe surrounding the rodlike notochord. • Pairs of cartilaginous projections extend dorsally, partially enclosing the nerve cord with what might be a vestige of an early stage vertebral column. • Both hagfishes and lampreys lack skeletonsupported jaws and paired appendages. • The brain and cranium evolved first in the vertebrate lineage. • This was followed by the vertebral column. • The jaws, ossified skeleton, and paired appendages evolved later. • This interpretation is consistent with the early Cambrian fossils in Chinese strata. Introduction to the Fishes
• Class Chondrichthyes (the cartilaginous fishes) and Class Osteichthyes (bony fishes) • In addition to jaws, fishes have two pairs of fins. • Research in developmental genetics has shown that differential expression of some Hox genes may determine whether one or two sets of appendages develop in the embryos of extant vertebrates. • Jaws and paired fins were major evolutionary breakthroughs.
• Jaws, with the help of teeth, enable the animal to grip food items firmly and slice them up. • A jawed fish can exploit food supplies that were unavailable to earlier agnathans. • Paired fins, along with the tail, enable fishes to maneuver accurately while swimming. • With these adaptations, many fish species were active predators, allowing for the diversification of both lifestyles and nutrient sources. Class Chondrichthyes: Sharks and rays have cartilaginous skeletons
• The class Chondrichthyes, sharks and their relatives, have relatively flexible endoskeletons of cartilage rather than bone.
• In most species, parts of the skeleton are strengthened by mineralized granules, and the teeth are bony. • There are about 750 extant species, almost all in the subclass of sharks and rays, with a few dozen species in a second subclass the chimaeras, or ratfishes.
• All have well-developed jaws and paired fins. • The cartilaginous skeleton of these fishes is a derived characteristic, not a primitive one.
• The ancestors of Chondrichthyes had bony skeletons. • The cartilaginous skeleton evolved secondarily. • During the development of most vertebrates, the skeleton is first cartilaginous and then becomes ossified as hard calcium phosphate matrix replaces the rubbery matrix of cartilage. • The streamlined bodies of most sharks enable them to be swift, but not maneuverable swimmers.
• Powerful axial muscles power undulations of the body and caudal fin to drive the fish forward. • The dorsal fins provide stabilization. • While some buoyancy is provided by low density oils in large livers, the flow of water over the pectoral and pelvic fins also provides lift to keep the animal suspended in the water column. Fig. 34.11a • Most sharks are carnivores that swallow their prey whole or use their powerful jaws and sharp teeth to tear flesh from animals too large to swallow.
• In contrast, the largest sharks and rays are suspension feeders that consume plankton. • Shark teeth probably evolved from the jagged scales. • The intestine of shark is a spiral valve, a corkscrewshaped ridge that increases surface area and prolongs the passage of food along the short digestive tract.
Fig. 34.11b • Acute senses are adaptations that go along with the active, carnivorous lifestyle of sharks.
• Sharks have sharp vision but cannot distinguish colors. • Their acute olfactory sense (smelling) occurs in a pair of nostrils. • Sharks can detect electrical fields, including those generated by the muscle contractions of nearby prey, through patches of specialized skin pores. • The lateral line system, a row of microscopic organs sensitive to pressure changes, can detect low frequency vibrations. • In sharks, the whole body transmits sound to the hearing organs of the inner ear. Class Osteichthyes: The existing classes of bony fishes are the ray-finned fishes, the lobe-finned fishes, and the lungfishes
• Bony fishes are the most numerous group of vertebrates, both in individuals and in species (about 30,000 species). • They range in size from 1 cm to more than 6 m. • They are abundant in the seas and in nearly every freshwater habitat. • Traditionally, all bony fishes were combined into a single class, Osteichthyes, but most systematists now recognize three extant classes: the ray-finned fishes, the lobe-finned fishes, and the lungfishes. • Nearly all bony fishes have an ossified endoskeleton with a hard matrix of calcium phosphate. • The skin is often covered with thin, flattened bony scales. • Like sharks, fishes can detect water disturbances through the lateral line system, part of which is visible as a row of tiny pits along either side of the body. • Bony fishes breathe by drawing water over four or five pairs of gills located in chambers covered by a protective flap, the operculum.
• Water is drawn into the mouth, through the pharynx, and out between the gills by movements of the operculum and muscles surrounding the gill chambers. Fig. 34.13 • Most fishes have an internal, air-filled sac, the swim bladder. • The positive buoyancy provided by air counters the negative buoyancy of the tissues, enabling many fishes be neutrally buoyant and remain suspended in the water. • Bony fishes are generally maneuverable swimmers.
• Their flexible fins are better for steering and propulsion than the stiffer fins of sharks. • The fastest bony fishes can swim up to 80 km/hr in short bursts. 4. Tetrapods evolved from specialized fishes that inhabited shallow water
• Amphibians were the first tetrapods to spend a substantial portion of their time of land. • However, there were earlier vertebrate tetrapods that had relatively sturdy, skeleton-supported legs instead of paired fins, and which lived in shallow aquatic habitats. Class Amphibia: Salamanders, frogs, and caecilians are the three existing amphibian orders
• Today the amphibians (Class Amphibia) are represented by about 4,800 species of salamanders (urodeles), anurans (tail-less ones”), and caecilians (leg-less ones) • Skin is moist, containing mucous glands and lacking epidermal scales • In lab, notice that the skin of an amphibian is smooth. Class Reptilia: Lizards, snakes, crocodilians, turtles, and birds. • Lacking mucus glands, covered with epidermal scales • Class Aves: forelimbs modified for flight, feathers present. Since birds are in the same clade as reptiles, they are often placed within the class Reptilia. Class Mammalia: Mammals • Mammary glands and hair present • Monotremes: Australia and New Guinea
• Platypus and two species of spiny anteaters Marsupial mammals: opossums, kangaroos, koalas Eutherian (placental) mammals: placentas are more complex than marsupial mammals Vertebrata: Presence of bony or cartilaginous vertebrae surrounding the nerve cord in living forms and have a notochord in all embryos and persisting to varying degrees. ...
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This note was uploaded on 01/15/2011 for the course BIOL 51 taught by Professor Janetkoprivnikar,greggd.jongeward during the Spring '08 term at Pacific.
- Spring '08