eucoelomate More protostomes (Annelids and Mollusks)
Porifera Cnidaria Platy- Nematoda Arthropoda Annelida Mollusca helminthes Echino- Chordata dermata
phylum Annelida (little rings; segmented worms)
About 15,000 described species in most habitats (marine, freshwater, terrestrial; primarily free-living). Structurally diverse but all share several common features:
Protostoma
Deuterostoma development pattern
Pseudocoelomates
Eucoelomates
Organ system level of organization, cephalization, bilateral symmetry; complete gut circulatory system (overcomes diffusion limitations) hydrostatic skeleton, circular and longitudinal muscles (good control of movement) -- nematodes have only longitudinal muscles and are restricted to a `thrashing' motion.
Acoelomates Radiata Parazoa Bilateria Eumetazoa
the nature of the body cavity other Bilateria presence or absence of a body cavity
fundamental symmetry and number of germ layers
levels of cell & tissue organization Protistan ancestor
phylum Annelida (little rings; segmented worms) Segmentation, segments separated by septa (each segment has replicated functions such as nerve ganglia and excretory organs, but is coordinated with the rest of the animal).
septum segments Coelom
phylum Annelida (little rings; segmented worms)
Three major classes: Oligochaeta, mainly freshwater and moist terrestrial habitats (example: earthworms) small setae (spines) in pairs in each segment small and unspecialized head Segments relatively undifferentiated Abundant, ecologically important, especially in soil. Generally hermaphroditic and egg-laying; hatchlings like miniature adults (no distinct larval stage).
Functional attributes of annelid body plan:
Gippsland giant earthworm (Australia)
Gut, lined with mesoderm
Segmentation, hydrostatic skeleton, nerve net, and bidirectional antagonistic muscles --> better movement control than in nematodes. coelom permits internal storage of specialized organs. no cuticle, so vulnerable to water loss and restricted to aquatic and moist terrestrial habitats.
phylum Annelida (little rings; segmented worms) Polychaeta, mainly marine; very diverse structurally well-developed head, often with elaborate feeding organs or tentacles. parapodia (fleshy flaps or extensions) on each segment, as well as setae -- spines, often large (top view):
phylum Annelida (little rings; segmented worms) Polychaeta Generally sexual larval stage (trochophore) is charcteristic. Very different from adult; generally planktonic.
band of cilia
mouth stomach anus intestine
Ecologically diverse: scavengers, predators, filter-feeders; some planktonic, others burrowing, others crawl around, some swim.
Feeding organs on head Parapodia with setae
Parapoida function in locomotion (swimming, crawling, burrowing) and gas exchange (large surface area)
phylum Annelida (little rings; segmented worms)
phylum Annelida (little rings; segmented worms)
Hirudinea (leeches), mainly freshwater and moist terrestrial habitats. Highly modified (derived from oligochaetes): body flattened (but can expand to hold a large meal) no setae or parapoida segmentation reduced (and undifferentiated) coelom largely filled with mesenchyme (largely acellular)
suckers
Hirudinea (leeches) Predators, scavengers, or parasites -- often on blood of vertebrates (cutting 'teeth' and anesthetics and anticoagulants in saliva; large capacity for blood). Still used medically (in fact, undergoing such a revival for microsurgery etc. that several companies sell them and some leech populations are endangered!)
Different locomotion from other annelids: suckers (modified segments) at both ends used in an 'inchworm' crawling pattern (some swim well).
phylum Mollusca
phylum Mollusca
Mollusks ("mollis" = soft) are structurally complex and very successful: about 80,000 species Standard protostomate characters (schizocoely, etc.) Unique, highly variable body plan. Ancestry uncertain, probably derived from annelids (some shared features) or flatworm-like ancestor. Like some annelids, many mollusks have trochopore larvae:
Main features of mollusk body plan: Calcified shells (greatly reduced or lost in some classes) No segmentation Circulatory system, reduced coelom (some use hemocoel for hydrostatic skeleton) Body plan based on foot, mantle, and visceral mass Because mollusk anatomy is so strange and variable, it's useful to consider its probable evolutionary history. Body plan is often thought to derive from hypothetical ancestral mollusk ("HAM") with these features:
phylum Mollusca
phylum Mollusca
Features of the hypothetical ancestral mollusk ("HAM")
calcified shell head with sense organs radula mantle tissue visceral mass (gut) anus mantle cavity gill, or ctenidia (ciliated)
Features of the hypothetical ancestral mollusk ("HAM")
calcified shell head with sense organs radula mantle tissue visceral mass (gut) anus mantle cavity gill, or ctenidia (ciliated)
foot
foot
Shell (one or several pieces) secreted by fleshy mantle Mouth has tongue-like radula with rasping teeth (used to scrape food off of rocks) Muscular foot for locomotion and support of visceral mass. Mantle cavity contains anus and ciliated gill (ctenidia).
Head, foot, shell, and mantle are highly modified in structure and organization in various classes of mollusks. We cover four of the most important: chitons, gastropods, bivalves, and cephalopods. These have great differences in form and function.
phylum Mollusca hypothetical ancestral mollusk ("HAM")
phylum Mollusca GASTROPODS: class Gastropoda; snails, slugs, nudibranchs, etc. Major modification is torsion: 180-degree counter-clockwise twist of "upper" portions of the body relative to the foot (occurs by asymmetrical growth during larval development).
CHITONS: class Polyplacophora ("many shell bearing")
Grazing animals that cling to rock surfaces; all marine. multiple calcified Body symmetrical plates trochophore larvae multiple calcified plates; head Visceral mass body slightly flexible Mantle cavity along each side of foot, multiple gills
radula foot gills in mantle cavity mantle tissue anus
"HAM" torsion plane
gill mantle cavity
anus heart
shell
gut head with sensory tentacles foot foot mouth with radula
phylum Mollusca GASTROPODS: class Gastropoda; snails, slugs, nudibranchs, etc.
phylum Mollusca GASTROPODS: class Gastropoda; snails, slugs, nudibranchs, etc.
Torsion introduces asymmetry but does two useful things: 1. lowers center of gravity (helps keep animal anchored during wave action, currents, etc.) 2. When attacked, gastropods pull body into the protective shell (into mantle cavity). Torsion insures that the head enters first, not last many gastropods have a `hatch cover' (operculum) on the foot. It plugs the shell opening when the body is retracted.
Very diverse; many modifications of body; many species:
in terrestrial slugs and snails, gill has
evolved into lung (air breathing).
foot
Terrestrial slugs and nudibranchs (marine slugs) have lost shell
(nudibranchs often colorful and poisonous)
Leopard slug banana slug (proud mascot of UCSC!)
phylum Mollusca GASTROPODS: class Gastropoda; snails, slugs, nudibranchs, etc.
phylum Mollusca BIVALVES: class Bivalvia; clams, scallops, oysters, mussels, etc. Two shells connected with hinge and closed with muscle (not shown); generally sedentary and often burrowing shell (one shell removed) Foot formed into digging tool
gut anus
Very diverse; many modifications of body; many species:
in terrestrial slugs and snails, gill has
evolved into lung (air breathing).
foot
Terrestrial slugs and nudibranchs (marine slugs) have lost shell
(nudibranchs often colorful and poisonous)
In some, radula has evolved into a drill or even a hypodermic
siphons bring water to buried animal. Some live on the substrate; a few mouth (scallops) swim clumsily. Head much reduced Gill used for filter-feeding and gas exchange. Food conveyed to mouth by labial palp (not shown; like a tentacle) geoduck clam
(Puget Sound)
siphons
foot mantle cavity gill
needle for injecting venom (cone shells).
phylum Mollusca CEPHALAPODS: class Cephalapoda; nautilus, squids, octopus, cuttlefish
phylum Mollusca CEPHALAPODS: class Cephalapoda; nautilus, squids, octopus, cuttlefish Body highly modified from "HAM" but still has the same basic parts (this is a squid, simplified): shell (external in nautilus, internal in cuttlefish, almost lost in squid, octopus)
large eyes head mantle
gut
Most highly derived mollusks; largest invertebrates -- giant squid can be 15-20 meters long and weigh a half-ton or so. Very different life style from most mollusks: motile, active, and agile (squids especially are excellent swimmers). Good vision (giant squid has largest eyes of any animal). Cuttlefish, squids, and octopi are active predators with excellent sense organs and large 'brain'. Easily the most intelligent of invertebrates. Some are highly social, with complex communication systems (color and form). Very important in marine ecosystems as predators and food sources.
"arms" (tentacles) beak (mouth)
gill siphon
heart
mantle cavity
phylum Mollusca CEPHALAPODS: class Cephalapoda; nautilus, squids, octopus, cuttlefish
gut
Last major lineage to consider: Deuterostomes
Porifera Cnidaria Platy- Nematoda Arthropoda Annelida Mollusca helminthes Echino- Chordata dermata
Protostoma
Deuterostoma development pattern
Tentacles and 'head' derived from foot (cephalopod: "head-foot") beak (and radula) in the center of ring of tentacles; often connected to venom glands (octopus, cuttlefish) Siphon (rolled-up piece of foot) can direct a water jet (expelled from mantle cavity by contractions of mantle) for rapid `jet propulsion' -- although 'backwards' with respect to the head.
Parazoa
Pseudocoelomates
Eucoelomates
Acoelomates Radiata Bilateria Eumetazoa
the nature of the body cavity other Bilateria presence or absence of a body cavity
fundamental symmetry and number of germ layers
levels of cell & tissue organization Protistan ancestor
The deuterostomes: Echinoderms & Chordates Like protostomes, deuterstomes are triploblastic and eucoelomate. But they differ in the pattern of development:
Protostomata cleavage Spiral, determinate (cell fates established early in development) Ectodermal, from cells near blastopore Schizocoely (blocks of mesoderm split internally to form coelom) the mouth; anus forms secondarily Deuterostomata Radial, indeterminate (cell fates established late in development) Endodermal, from archenteron `outpocket' From gut, by enterocoely (archenteron outpocket `pinches off' to form coelom) the anus; mouth forms secondarily
The deuterostomes: Echinoderms & Chordates
Deuterostome development: formation of mesoderm and coelom
Gastrulation
Blastocoel
Mesoderm formation Origin of coelom Blastopore forms:
Blastopore forms anus, mouth forms secondarily, hence, deuterostomes (deutero = "second", stome = "mouth")
The deuterostomes: Echinoderms & Chordates
Deuterostome development: formation of mesoderm and coelom
The deuterostomes: Echinoderms & Chordates
Deuterostome development: formation of mesoderm and coelom
Mesoderm begins to form from outpockets of the early gut: enterocoely (from endoderm)
Mesoderm begins to form from outpockets of the early gut: enterocoely (from endoderm)
Blastopore forms anus, mouth forms secondarily, hence, deuterostomes (deutero = "second", stome = "mouth")
Blastopore forms anus, mouth forms secondarily, hence, deuterostomes (deutero = "second", stome = "mouth")
The deuterostomes: Echinoderms & Chordates
Deuterostome development: formation of mesoderm and coelom
MAKE SURE YOU UNDERSTAND:
basic anatomy of annelids -- segmentation; function of coelom as hydrostatic skeleton characteristics of oligochaetes, polychaetes, hirudinea (functional modifications of each) mollusk body plan; HAM; foot, mantle, visceral mass characteristics of chitons characteristics of gastropods: torsion and its function; shelled and shell-less forms characteristics of bivalves: modifications for burrowing and filter-feeding characteristics of cephalopods: modifications for active predatory life style key deuterostome characters (cleavage, mesoderm & coelom formation, etc.)
mouth
Ectoderm Mesoderm Coelom (from gut: Enterocoely)
Mesoderm eventually completely lines the coelom (eucoelomate)
Endoderm
Gut lumen
anus