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 Protostomes Trochophores Flatworms, rotifers, molluscs, and annelids Either have trochophore larvae today or an ancestor had one on the past cilia trochophore larva

Page 627 cilia trochophore larva Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 gastrovascular cavity eyespots 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

© Tom E. Adams/Peter Arnold 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 cilia a. Digestive system: Three-branched system flame cell excretory canal excretory pore b. Excretory system: Flame-cell system ovary yolk gland sperm duct testis genital pore c. Reproductive system: Hermaphroditic system brain lateral nerve cord transverse nerve d. Nervous system: Ladder-style system auricle eyespots © Tom E. Adams/Peter Arnold e. 5 mm 6

30.3 The Trochozoa Parasitic Flatworms Primary and secondary hosts 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 scolex sucker 2. Bladder worm attaches to human intestine where it matures into a tapeworm. 1.0 mm 250 m 3. As the tapeworm grows, proglottids mature, and eventually fill with eggs. 4. Eggs leave the primary host in feces, which may contaminate water or vegetation. 5. Livestock may ingest the eggs, becoming a secondary host as each larva becomes a bladder worm encysted in muscle. 6. Rare or uncooked meat from secondary host contains many bladder worms. 1. Primary host ingests meat containing bladder worms. (proglottid): © John D. Cunningham/Visuals Unlimited; (scolex): © James Webb/Phototake

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 Schistosomiasis, an infection of humans caused by blood flukes, is an extremely prevalent disease in Egypt – especially since the building of the Aswan High Dam. Standing water in irrigation ditches, combined with unsanitary practices, has created the conditions for widespread infection.

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 shell eyes tentacles on mantle valve Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. shell eyes tentacles on mantle valve b. Scallop, Pecten sp. eye tentacle gills arm 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 foot a. Land snail © Farley Bridges; 18

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

Fig. 30.11d fin pen mantle suckers gill ink sac arm anus funnel eye Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 30.11d fin pen mantle suckers gill ink sac arm anus funnel eye tentacle

© Georgette Douwma/Photo Researchers, Inc. Fig. 30.11e Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. fins eye tentacles with suckers 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 cerebral ganglion fin pen mantle suckers gill tentacle ink sac arm radula anus pedal ganglion funnel penis eye growth line fins tentacles with suckers eye eyes foot spiral shell foot tentacle a. Land snail b. Squid a: © Farley Bridges; b: © Georgette Douwma/Photo Researchers, Inc. 27

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 pericardial cavity umbo anterior aorta heart kidney 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 stomach posterior adductor muscle anterior adductor muscle posterior aorta esophagus shell anterior ganglion anus mouth excurrent siphon labial palps foot ganglion incurrent siphon foot gill gonad intestine mantle

Scallop-adductor muscle

Oyster bed

Oyster

Pearls

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

Polychaetes 30.3 The Trochozoa Have many setae or bristles Anchor worm or help in locomotion Used for swimming and respiration Active predators or sessile forms Trochophore larva

© Heather Angel/Natural Visions; Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. sensory projections parapodia a. Clam worm, Nereis © Heather Angel/Natural Visions;

a: © Heather Angel/Natural Visions; c: © Diane R. Nelson 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

a. pharynx brain mouth esophagus coelom hearts (5 pairs) crop 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.

coelomic lining longitudinal muscles Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. dorsal blood vessel coelomic lining longitudinal muscles muscular wall of intestine circular muscles nephridium typhlosole setae coelom ventral blood vessel cuticle excretory pore ventral nerve cord subneural blood vessel b.

© Roger K. Burnard/Biological Photo Service 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