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Chapters 33 - 55 - CHAPTER 33 INVERTEBRATES OUTLINE I II...

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Unformatted text preview: CHAPTER 33 INVERTEBRATES OUTLINE I. II. The Parazoa A. Phylum Porifera: sponges are sessile with porous bodies and choanocytes The Radiata A. Phylum Cnidaria: cnidarians have radial symmetry, a gastrovascular cavity, and cnidocytes B. Phylum Ctenophora: comb jellies possess rows of ciliary plates and adhesive colloblasts The Acoelomates A. Phylum Platyhelminthes: flatworms are dorsoventrally flattened acoelomates The Pseudocoelomates A. Phylum Rotifera: rotifers have jaws and a crown of cilia B. Phylum Nematoda: roundworms are unsegmented and cylindrical with tapered ends The Coelomates: Protostomes A. Phylum Nemertea: The phylogenetic position of proboscis worms is uncertain B. The lophophorate phyla: bryozoans, phoronids, and brachiopods have ciliated tentacles around their mouths C. Phylum Mollusca: mollusks have a muscular foot, a visceral mass, and a mantle D. Phylum Annelida: annelids are segmented worms E. Phylum Arthropoda: arthropods have regional segmentation, jointed appendages, and an exoskeleton The Coelomates: Deuterostomes A. Phylum Echinodermata: Echinoderms have a water vascular system and secondary radial symmetry B. Phylum Chordata: the chordates include two invertebrate subphyla and all vertebrates III. IV. V. VI. OBJECTIVES After reading this chapter and attending lecture, the student should be able to: 1. From a diagram, identify the parts of a sponge and describe the function of each including the spongocoel, porocyte, epidermis, choanocyte, mesohyl, amoebocyte, osculum, and spicule. 2. List characteristics of the phylum Cnidaria that distinguish it from the other animal phyla. 3. Describe the two basic body plans in Cnidaria and their role in Cnidarian life cycles. 4. List the three classes of Cnidaria and distinguish among them based upon life cycle and 476 Unit V The Evolutionary History of Biological Diversity 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. morphological characteristics. List characteristics of the phylum Ctenophora that distinguish it from the other animal phyla. List characteristics that are shared by all bilaterally symmetrical animals. List characteristics of the phylum Platyhelminthes that distinguish it from the other animal phyla. Distinguish among the four classes of Platyhelminthes and give examples of each. Describe the generalized life cycle of a trematode and give an example of one fluke that parasitizes humans. Describe the anatomy and generalized life cycle of a tapeworm. List distinguishing characteristics descriptive of the phylum Nemertea. Explain why biologists believe proboscis worms evolved from flatworms. Describe features of digestive and circulatory systems that have evolved in the Nemertea and are not found in other acoelomate phyla. Describe unique features of rotifers that distinguish them from other pseudocoelomates. Define parthenogenesis and describe alternative forms of rotifer reproduction. List characteristics of the phylum Nematoda that distinguish it from other pseudocoelomates. Give examples of both parasitic and free-living species of nematodes. List characteristics that distinguish the phylum Mollusca from the other animal phyla. Describe the basic body plan of a mollusk and explain how it has been modified in the Polyplacophora, Gastropoda, Bivalvia, and Cephalopoda. Distinguish among the following four Molluscan classes and give examples of each: a. Polyplacophora c. Bivalvia b. Gastropoda d. Cephalopoda Explain why some zoologists believe the mollusks evolved from ancestral annelids while others propose that mollusks arose from flatworm-like ancestors. List characteristics that distinguish the phylum Annelida from the other animal phyla. Explain how a fluid-filled septate coelom is used by annelids for burrowing. Distinguish among the classes of annelids and give examples of each. List characteristics of arthropods that distinguish them from the other animal phyla. Describe advantages and disadvantages of an exoskeleton. Distinguish between hemocoel and coelom. Provide evidence for an evolutionary link between the Annelida and Arthropoda. Describe major independent arthropod lines of evolution represented by the subphyla: a. Trilobitomorpha c. Crustacea b. Cheliceriformes d. Uniramia Explain what arthropod structure was a preadaptation for living on land. Distinguish among the following arthropod classes and give an example of each: a. Arachnida d. Chilopoda b. Crustacea e. Insecta c. Diplopoda Distinguish between incomplete metamorphosis and complete metamorphosis. Define lophophore and list three lophophorate phyla. Explain why lophophorates are difficult to assign as protostomes or deuterostomes. List at least four characteristics shared by the deuterostome phyla that distinguish them from protostomes. Chapter 33 Invertebrates 477 36. 37. 38. List characteristics of echinoderms that distinguish them from other animal phyla. Describe the structures and function of a water vascular system, including ring canal, radial canal, tube feet and ampulla. Distinguish among the classes of echinoderms and give examples of each. KEY TERMS invertebrates spongocoel osculum choanocyte mesohyl amoebocyte hermaphrodites gastrovascular cavity polyp medusa cnidocytes cnidae radula Class Arachnida complete digestive tract parthenogenesis closed circulatory system lophophorate animals lophophore bryozoans phoronids brachiopods foot visceral mass mantle mantle cavity eurypterids planarian ammonites Class Chilopodia cuticle exoskeleton molting open circulatory system trilobite Chelicerates Uniramians Crustaceans chelicerae mandibles antennae compound eyes colloblasts torsion Class Diplodia Class Insecta entomology Malpighian tubules tracheal system incomplete metamorphosis complete metamorphosis echinoderms water vascular system tube feet nematocysts trochophore book lungs metanephridia LECTURE NOTES Over one million species of animals are living today; 95% of these are invertebrates. • Most are aquatic. • The most familiar belong to the subphylum Vertebrata of the phylum Chordata. This is only about 5% of the total. I. The Parazoa A. Phylum Porifera: sponges are sessile with porous bodies and choanocytes The sponges, in the phylum Porifera, are the only members of the subkingdom Parazoa due to their unique development and simple anatomy (see Campbell, Figure 33.1). • Approximately 9000 species, mostly marine with only about 100 in fresh water • Lack true tissues and organs, and contain only two layers of loosely associated unspecialized cells • No nerves or muscles, but individual cells detect and react to environmental changes • Size ranges from 1 cm to 2 m • All are suspension-feeders (= filter-feeders) • Possibly evolved from colonial choanoflagellates Parts of the sponge include (see Campbell, Figure 33.2): • Spongocoel = Central cavity of sponge • Osculum = Larger excurrent opening of the spongocoel • Epidermis = S ingle layer of flattened cells which forms outer surface of the sponge 478 Unit V The Evolutionary History of Biological Diversity Porocyte = Cells which form pores; possess a hollow channel through the center which extends from the outer surface (incurrent pore) to spongocoel • Choanocyte = Collar cell, majority of cells which line the spongocoel; possess a flagellum which is ringed by a collar of fingerlike projections. Flagellar movement moves water and food particles which are trapped on the collar and later phagocytized. • Mesohyl = T he gelatinous layer located between the two layers of the sponge body wall (epidermis and choanocytes) • Amoebocyte = Wandering, pseudopod bearing cells in the mesohyl; function in food uptake from choanocytes, food digestion, nutrient distribution to other cells, formation of skeletal fibers, gamete formation • Spicule = S harp, calcium carbonate or silica structures in the mesohyl which form the skeletal fibers of many sponges • Spongin = Flexible, proteinaceous skeletal fibers in the mesohyl of some sponges Most sponges are hermaphrodites, but usually cross-fertilize. • Eggs and sperm form in the mesohyl from differentiated amoebocytes or choanocytes. • Eggs remain in the mesohyl. • Sperm are released into excurrent flow of the spongocoel and are then drawn in with incurrent flow of another sponge. • Sperm penetrate into mesohyl and fertilize the eggs. • The zygote develops into a flagellated larva which is released into the spongocoel and escapes with the excurrent water through the osculum. • Surviving larvae settle on the substratum and develop. In most cases the larva turns inside-out during metamorphosis, moving the flagellated cells to the inside. Sponges possess extensive regeneration abilities for repair and asexual reproduction. II. The Radiata The branch radiata is composed of phylum Cnidaria and phylum Ctenophora A. Phylum Cnidaria: Cnidarians have radial symmetry, a gastrovascular cavity, and cnidocytes There are more than 10,000 species in the phylum Cnidaria, most of which are marine. The phylum contains hydras, jellyfish, sea anemones and coral animals. Some characteristics of cnidarians include: • Radial symmetry • Diploblastic • Simple, sac-like body • Gastrovascular cavity, a c entral digestive cavity with only one opening (functions as mouth and anus) There are two possible cnidarian body plans: sessile polyp and motile, floating medusa (see Campbell, Figure 33.3). Some species of cnidarians exist only as polyps, some only as medusae, and others are dimorphic (both polyp and medusa stages in their life cycles). Polyp = Cylindrical form which adheres to the substratum by the aboral end of the body stalk and extends tentacles around the oral end to contact prey • Chapter 33 Invertebrates 479 Medusa = Flattened, oral opening down, bell-shaped form; moves freely in water by passive drifting and weak bell contractions; tentacles dangle from the oral surface which points downward. Cnidarians are carnivorous. • Tentacles around the mouth/anus capture prey animals and push them through the mouth/anus into the gastrovascular cavity. • Digestion begins in the gastrovascular cavity with the undigested remains being expelled through the mouth/anus. • Tentacles are armed with stinging cells, called cnidocytes—after which the Cnidaria are named. Cnidocytes = Specialized cells of cnidarian epidermis that contain eversible capsule-like organelles, or c nidae, used in defense and capture of prey (see Campbell, Figure 33.4). Nematocysts are stinging capsules. The simplest forms of muscles and nerves occur in the phylum Cnidaria. • Epidermal and gastrodermal cells have bundles of microfilaments arranged into contractile fibers. ⇒ T he gastrovascular cavity, when filled with water, acts as a hydrostatic skeleton against which the contractile fibers can work to change the animal's shape. • A simple nerve net coordinates movement; no brain is present. ⇒ T he nerve net is associated with simple sensory receptors radially distributed on the body. This permits stimuli to be detected and responded to from all directions. There are three major classes of cnidarians (see Campbell, Figure 33.5 and Table 33.1): 1. Class Hydrozoa Most hydrozoans alternate polyp and medusa forms in the life cycle although the polyp is the dominant stage. Some are colonial (e.g., Obelia, Campbell, Figure 33.6), while others are solitary (e.g., Hydra ). Hydra is unique in that only the polyp stage is present. • They usually reproduce asexually by budding; however, in unfavorable conditions they reproduce sexually. In this case a resistant zygote is formed and remains dormant until environmental conditions improve. 2. Class Scyphozoa The planktonic medusa (jellyfish) is the most prominent stage of the life cycle. • Coastal species usually pass through a small polyp stage during the life cycle. • Open ocean species have eliminated the polyp entirely. 3. Class Anthozoa This class contains sea anemones and coral animals. They only occur as polyps. Coral animals may be solitary or colonial and secrete external skeletons of calcium carbonate. • Each polyp generation builds on the skeletal remains of earlier generations. In this way, coral reefs are formed. • Coral is the rock-like external skeletons. 480 Unit V The Evolutionary History of Biological Diversity B. Phylum Ctenophora: combjellies possess rows of ciliary plates and adhesive colloblasts This phylum contains the comb jellies. There are about 100 species, all of which are marine. Some characteristics of ctenophores include: • A resemblance to the medusa of Cnidarians in that the body of most is spherical or ovoid; a few are elongate and ribbonlike. • Transparent body, 1 - 10 cm in diameter (spherical/ovoid forms) or up to 1 m long (ribbonlike forms) (see Campbell, Figure 33.7) • Eight rows of comblike plates composed of fused cilia which are used for locomotion • One pair of long retractable tentacles that function in capturing food; these tentacles have adhesive structures called colloblasts. • A sensory organ containing calcareous particles is present. ⇒ T he particles settle to the low point of the organ which then acts as an orientation cue. ⇒ N erves extending from the sensory organ to the combs of cilia coordinate movement. III. The Acoelomates A. Phylum Platyhelminthes: flatworms are dorsoventrally flattened acoelomates The members of the phylum Platyhelminthes differ from the phylum Cnidaria in that they: • Exhibit bilateral symmetry with moderate cephalization • Are triploblastic (develop from three-layered embryos: ectoderm, endoderm and mesoderm) • Possess several distinct organs, organ systems, and true muscles Although more advanced than cnidarians, two things point to the early evolution of platyhelminths in bilateria history. • A gastrovascular cavity is present. • They have an acoelomate body plan. There are more than 20,000 species of Platyhelminthes which are divided into four classes (see Campbell, Table 33.2): • Class Turbellaria • Classes Trematoda and Monogenea • Class Cestoda 1. Class Turbellaria Mostly free-living, marine species; a few species are found in freshwater and moist terrestrial habitats (see Campbell, Figure 33.8). Planarians are familiar and common freshwater forms (see Campbell, Figure 33.9). • Carnivorous, they feed on small animals and carrion • Lack specialized organs for gas exchange or circulation ⇒ Gas exchange is by diffusion (flattened body form places all cells close to water). ⇒ Fine branching gastrovascular cavity distributes food throughout the animal. • Flame cell excretory apparatus present which functions primarily t o maintain osmotic balance of the animal. Chapter 33 Invertebrates 481 ⇒ Nitrogenous waste (ammonia) diffuses directly from cells to the water. • Move by using cilia on the ventral dermis to glide along a film of mucus. Muscular contractions produce undulations which allow some to swim. • On the head are a pair of eyespots which detect light and a pair of lateral auricles that are olfactory sensors. ⇒ Possess a rudimentary brain which is capable of simple learning. • Reproduce either asexually or sexually. ⇒ A sexually by regeneration: mid-body constriction separates the parent into two halves, each of which regenerates the missing portion ⇒ Sexually by cross-fertilization of these hermaphroditic forms 2. Classes Monogenea and Trematoda All members of these two classes are parasitic. Flukes are members of the class Trematoda. • Suckers are usually present for attaching to host internal organs. • Primary organ system is the reproductive system; a majority are hermaphroditic. • Life cycles include alternations of sexual and asexual stages with asexual development taking place in an intermediate host. ⇒ L arvae produced by asexual development infect the final hosts where maturation and sexual reproduction occurs (see Campbell, Figure 33.10) • Schistosoma spp. (blood flukes) infect 200 million people worldwide. Members of the class Monogenea are mostly external parasites of fish. • Structures with large and small hooks are used for attaching to the host animal. • All are hermaphroditic and reproduce sexually. 3. Class Cestoidea Adult tapeworms parasitize the digestive system of vertebrates. • Possess a scolex (head) which may be armed with suckers and/or hooks that help maintain position by attaching to the intestinal lining (see Campbell, Figure 33.11). • Posterior to the scolex is a long ribbon of units called proglottids. ⇒ A proglottid is filled with reproductive organs. • No digestive system is present. The life cycle of a tapeworm includes an intermediate host. • Mature proglottids filled with eggs are released from the posterior end of the worm and pass from the body with the feces. • Eggs are eaten by an intermediate host and a larva develops, usually in muscle tissue. ⇒ T he final host becomes infected when it eats an intermediate host containing larvae. • Humans can become infected with some species of tapeworms by eating undercooked beef or pork containing larvae. IV. The Pseudocoelomates The pseudocoelomate body plan probably arose independently several times. 482 Unit V The Evolutionary History of Biological Diversity A. Phylum Rotifera: rotifers have jaws and a crown of cilia There are approximately 1800 species of rotifers. They are small, mainly freshwater organisms, although some are marine and others are found in damp soil. • Size ranges from 0.05-2.0 mm • Pseudocoelomate with the pseudocoelomic fluid serving as a hydrostatic skeleton and as a medium which transports nutrients and wastes when the body moves • Complete digestive system is present. ⇒ R otifer refers to the crown of cilia that draws a vortex of water into the mouth. ⇒ P osterior to the mouth, a jawlike organ grinds the microscopic food organisms suspended in the water. Reproduction in rotifers may be by parthenogenesis or sexual. • Some species consist only of females with new females developing by parthenogenesis from unfertilized eggs. • Other species produce two types of eggs, one that develops into females, the other into degenerate males. ⇒ M ales produce sperm that fertilize eggs which develop into resistant zygotes that survive desiccation. ⇒ W hen conditions improve, the zygotes break dormancy and develop into a new female generation that reproduces by parthenogenesis until unfavorable conditions return. • Rotifers have no regeneration or repair abilities. Rotifers contain a certain and consistent number of cells as adults. The zygotes undergo a specific number of divisions and the adult contains a fixed number of cells. B. Phylum Nematoda: roundworms are unsegmented and cylindrical with tapered ends There are about 90,000 species of roundworms, ranging in size from less than 1.0 mm to more than 1 m. • Bodies are cylindrical with tapered ends • Very numerous in both species and individuals • Found in fresh water, marine, moist soil, tissues of plants, and tissues and body fluids of animals • A complete digestive tract is present and nutrients are transported through the body in the pseudocoelomic fluid • A tough, transparent cuticle forms the outer body covering (see Campbell, Figure 33.12a) • Longitudinal muscles are present and provide for whip-like movements • Dioecious with females larger than males • Sexual reproduction only, with internal fertilization • Female may produce 100,000 or more resistant eggs per day • Like rotifers, nematodes have a fixed number of cells as adults Nematodes fill various roles in the community. • Free-living forms are important in decomposition and nutrient cycling. • Plant parasitic forms are important agricultural pests. • Animal parasitic forms can be hazardous to health ( Trichinella spiralis in humans via undercooked infected pork) (see Campbell, Figure 33.13b). Chapter 33 Invertebrates 483 • V. One species, Caenorhabitis elegans, is cultured extensively and is a model species for the study of development. The Coelom...
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