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30.3 The Trochozoa • Bilaterally symmetrical at least in some stage of their development • As embryos, they have three germ layers • As adults, they have the organ level of organization cilia • Protostomes • Trochophores • Flatworms, rotifers, molluscs, and annelids trochophore larvathe • Either have trochophore larvae today or an ancestor had one on past Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Page 627 cilia trochophore larva 30.3 The Trochozoa • Flatworms: Phylum Platyhelminthes • Incomplete digestive tract and only one opening, the mouth • No body cavity – mesoderm fills spaces between organs • Free-living planarians • Have muscles and excretory, reproductive, and digestive systems. They have all organs except respiratory and circulatory organs (diffusion). • The flat body facilitates diffusion of oxygen and other molecules from cell to cell. Parasitic flukes and tapeworms 30.3 The Trochozoa • Free-living Flatworms • Freshwater planarians • Found in lakes, ponds, and streams • Feed on small organisms such as worms and crustaceans • Possesses an excretory system (flame cell system) • Ladder-like nervous system exhibits cephalization • Reproduce both asexually and sexually • Regeneration (asexual) • Hermaphroditic cross-fertilization (sexual) Planarian Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. gastrovascular cavity eyespots pharynx extended through mouth auricle a. Digestive system: Three-branched system Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Planarian Anatomy gastrovascular cavity eyespots pharynx extended through mouth auricle flame cell fluid a. Digestive system: Three-branched system cilia flame cell excretory canal excretory pore b. Excretory system: Flame-cell system ovary yolk sperm gland duct testis genital pore c. Reproductive system: Hermaphroditic system brain lateral nerve cord transverse nerve d. Nervous system: Ladder-style system eyespots auricle 5 mm e. © Tom E. Adams/Peter Arnold 30.3 The Trochozoa • Parasitic Flatworms • Tapeworms (class Cestoda) • • • • • Endoparasites Range in length from several millimeters to 20 meters Tough outer tegument to protect from host’s enzymes Scolex - has hooks for attachment; not a sucker Body of segments called proglottids • Organs of both sexes in each proglottid • Proglottids filled with fertilized eggs are called gravid • Primary and secondary hosts Life Cycle of a Tapeworm, Taenia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. hooks proglottid 2. Bladder worm attaches to human intestine where it matures into a tapeworm. 1. Primary host ingests meat containing bladder worms. 6. Rare or uncooked meat from secondary host contains many bladder worms. scolex 1.0 mm sucker 250 m 3. As the tapeworm grows, proglottids mature, and eventually fill with eggs. 5. Livestock may ingest the eggs, becoming a secondary host as each larva becomes a bladder worm encysted in muscle. (proglottid): © John D. Cunningham/Visuals Unlimited; (scolex): © James Webb/Phototake 4. Eggs leave the primary host in feces, which may contaminate water or vegetation. 30.3 The Trochozoa • Parasitic Flatworms • Flukes (class Trematoda) • Endoparasites of various vertebrates • Blood, liver and lung flukes • • • • • • Two suckers: one for feeding, one for attachment Alimentary canal is well developed Muscles and excretory system much like free-living flatworms Poorly developed senses Hermaphroditic Complex life cycle involving two intermediate hosts Schistosomiasis 30.3 The Trochozoa • Molluscs (phylum Mollusca) • Second most numerous animal phylum • Includes chitons, limpets, slugs, snails, abalones, conchs, nudibranchs, clams, scallops, squid, and octopuses • True coelom • Bilateral symmetry • 3 germ layers • Organ level of organization • Complete digestive tract 30.3 The Trochozoa • Molluscs • Unique characteristics of molluscs • Three distinct parts: • Visceral mass: includes most organs • Foot: muscular portion used for locomotion • Mantle: covering that almost encloses visceral mass • Mantle cavity - space between the two folds of the mantle • Mantle may secrete a shell • Radula - rasping organ for feeding Diversity of Molluscs Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. shell eyes tentacles on mantle valve b. Scallop, Pecten sp. tentacle eye arm gills mantle foot suckers c. Nudibranch, Glossodoris macfarlandi d. Two-spotted octopus, Octopus bimaculoides b: Courtesy Larry S. Roberts; c: © Kenneth W. Fink/Bruce Coleman, Inc.; d: © Ken Lucas/Visuals Unlimited 30.3 The Trochozoa • Gastropods (class Gastropoda) • • • • • Nudibranchs, conchs, and snails Foot is flattened ventrally Move by muscle contractions along the foot Some are herbivores, others carnivores Nudibranchs (sea slugs) • Lack shell • Conchs and snails have a shell • Protection • Prevents desiccation in land snails Nudibranchs Conch Shell Gastropod and Cephalopod Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. eye hermaphroditic gland shell cerebral ganglion tentacle radula pedal ganglion penis foot Gastropod and Cephalopod Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. growth line eyes spiral shell a. Land snail © Farley Bridges; foot 30.3 The Trochozoa • Cephalopods (class Cephalopoda) • Squid, octopus, nautilus • Foot has evolved into funnel or siphon • Powerful beak and radula for feeding • Cephalization is apparent • Octopuses have no shell, squid have reduced shell • Octopuses thought to be among the most intelligent invertebrates Squid Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 30.11d fin mantle pen suckers gill ink sac arm anus funnel eye tentacle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 30.11e tentacles with suckers fins eye b. Squid © Georgette Douwma/Photo Researchers, Inc. Octopus Octopus Giant Squid Swimming Nautilus Gastropod and Cephalopod Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. eye hermaphroditic gland shell fin cerebral ganglion pen mantle suckers gill tentacle ink sac arm radula anus pedal ganglion funnel penis eye growth line eyes foot spiral shell a. Land snail tentacles with suckers fins eye foot tentacle b. Squid a: © Farley Bridges; b: © Georgette Douwma/Photo Researchers, Inc. 30.3 The Trochozoa • Bivalves (class Bivalvia) • Clams, oysters, scallops, mussels • Two-part shells secreted by mantle • Filter-feeders: water enters through incurrent siphon • Visceral mass • Coelom is reduced • Pericardial cavity is the only remains of the coelom • Described as an open circulatory system because blood flows through sinuses in organs • Sexes separate – trochophore larvae in marine clams Clam, Anodonta Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. pericardial cavity umbo anterior aorta heart kidney posterior ganglion posterior retractor muscle digestive gland posterior adductor muscle stomach anterior adductor muscle posterior aorta esophagus shell anterior ganglion anus mouth excurrent siphon labial palps incurrent siphon foot ganglion foot gill gonad intestine mantle Scallop-adductor muscle 16-30 Oyster bed 16-31 Oyster 16-32 Pearls 16-33 30.3 The Trochozoa • Annelids (phylum Annelida) • • • • • • Only trochozoan with segmentation and a well-developed coelom Hydrostatic skeleton Specialization of digestive tract Closed circulatory system Brain with nerve cord connecting ganglia in each segement Excretory system – nephridia in most segements • Tubule for collecting waste material 30.3 The Trochozoa • Polychaetes • Have many setae or bristles • Anchor worm or help in locomotion • Used for swimming and respiration • Active predators or sessile forms • Trochophore larva Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. sensory projections parapodia a. Clam worm, Nereis © Heather Angel/Natural Visions; Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. sensory projections pharynx (extended) sensory projections jaw eyes parapodia parapodia a. Clam worm, Nereis b. Head region of Nereis spiraled tentacles c. Christmas tree worms, Spirobranchus a: © Heather Angel/Natural Visions; c: © Diane R. Nelson 30.3 The Trochozoa • Oligocaetes (class Oligochaeta) • • • • • • • Includes earthworms Few setae per segment Head is not well developed Gas exchange is across the body wall Scavengers on dead or living organic matter Evidence of segmentation in many systems Hemraphroditic • Clitellum • No larval stage Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. pharynx brain mouth esophagus coelom hearts (5 pairs) crop seminal vesicle dorsal blood vessel nephridium ventral blood vessel ventral nerve cord anus clitellum a. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. dorsal blood vessel coelomic lining circular muscles longitudinal muscles muscular wall of intestine nephridium typhlosole setae coelom ventral blood vessel ventral nerve cord subneural blood vessel b. cuticle excretory pore Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. clitellum anterior end clitellum anterior end c. © Roger K. Burnard/Biological Photo Service 30.3 The Trochozoa • Leeches (class Hirudinea) • • • • • Most live in freshwater No setae 2 suckers – one around mouth, large posterior one Some free-living but most are fluid feeders Hirudin prevents blood coagulation Leeches Medicinal Leeches