Platyhelminthes Flatworms - Dorsoventrally flattened Simplest bilaterally symmetrical organisms

1. Platyhelminthes • Flatworms - Dorsoventrally flattened • Simplest bilaterally symmetrical organisms • First organs and organ systems** • Central nervous system • Simple “brain” coordinates muscle movements • Incomplete digestive system • Mouth but no anus • Similar to Cnidaria and Ctenophora • Mesoderm** • Cell layer between endoderm and ectoderm • Gives rise to muscles, reproductive system

2. Platyhelminthes • Turbellaria • Mostly free-living carnivorous species • Most commonly seen (Why?) • Some live as commensal animals inside other invertebrates (oysters, crabs, etc.)

4. Platyhelminthes • Trematoda (Flukes) • Most species (6000) • Parasitic – Feed on tissues, blood, gut contents • Complex life cycles • Adults live in vertebrate host (fish, whale, bird) • Larvae may inhabit invertebrates (intermediate hosts) • Vertebrate eats intermediate host (clam, snail, etc.) • Cestoda (Tapeworms) • Parasitic • Live in vertebrate intestines • Head attaches to intestine wall with suckers or hooks • Gutless – absorb nutrients through body wall • May reach 50 feet!! (sperm whales)

5. Nemertea • Ribbon worms • Cosmopolitan • Most common in shallow, temperate regions • Complete digestive tract** • Mouth and anus • Circulatory system** • Use long, fleshy proboscis to capture prey • Feed on crustaceans and worms • May be cryptic or conspicuous • Can reach 30 m in length!!

6. Lophophorates • Three phyla – all animals possess lophophore • Ciliated hollow tentacles arranged in a horseshoe • Suspension feeders • Bilateral symmetry, coelom (body cavity), U-shaped gut • Ectoprocta – Bryozoans • Colonies consist of interconnected individual zooids • Encrusting and lacy forms (CaCO3 tests) • Retractable lophophore • Phoronida – Phoronids, Horseshoe Worms • Worm-shaped • Agglutinated sediment tubes attached to hard substrate in shallow water • Brachiopoda – Lamp Shells • Abundant in fossil record • Superficially resemble clams, but shells are dorsal-ventral, not left-right as in mollusks • Many attached to substrate with pedicle (short stalk)

7. Bryozoans

8. Lophophorates • Three phyla – all animals possess lophophore • Ciliated hollow tentacles arranged in a horseshoe • Suspension feeders • Bilateral symmetry, coelom (body cavity), U-shaped gut • Ectoprocta – Bryozoans • Colonies consist of interconnected individual zooids • Encrusting and lacy forms (CaCO3 tests) • Retractable lophophore • Phoronida – Phoronids, Horseshoe Worms • Worm-shaped • Agglutinated sediment tubes attached to hard substrate in shallow water • Brachiopoda – Lamp Shells • Abundant in fossil record • Superficially resemble clams, but shells are dorsal-ventral, not left-right as in mollusks • Many attached to substrate with pedicle (short stalk)

9. Lophophorates • Three phyla – all animals possess lophophore • Ciliated hollow tentacles arranged in a horseshoe • Suspension feeders • Bilateral symmetry, coelom (body cavity), U-shaped gut • Ectoprocta – Bryozoans • Colonies consist of interconnected individual zooids • Encrusting and lacy forms (CaCO3 tests) • Retractable lophophore • Phoronida – Phoronids, Horseshoe Worms • Worm-shaped • Agglutinated sediment tubes attached to hard substrate in shallow water • Brachiopoda – Lamp Shells • Abundant in fossil record • Superficially resemble clams, but shells are dorsal-ventral, not left-right as in mollusks • Many attached to substrate with pedicle (short stalk)

11. Corals • Biology • Phylum Cnidaria, Class Anthozoa (most) • Lack medusa stage • Hermatypic (reef building) corals produce skeletons made of calcium carbonate • Most contain mutualistic zooxanthellae (provide nutrition; enhance calcium carbonate deposition) • Many growth forms

14. Corals • Biology • Reproduction • Sexual: Most broadcast spawners; some brooders • Polyp Planula (planktonic larva)  Polyp • Asexual: Fragmentation (can be *very* important) • All polyps in a colony genetically identical

15. Fig. 15-4

16. Coral Reefs • Distribution • Living reefs ~ 600,000 km2 (0.17% of sea floor) • Great Barrier Reef = Largest • >2000 km long • Up to 145 km wide • Visible from space

17. Coral Reefs • Conditions • Substrate • Primarily in areas with hard substrate • Light - Bright (Why?) • Rarely develop in water > 50 m deep • Continental shelves, around islands, tops of seamounts • Temperature • Mean annual water temperature > 20 oC • Best development at 23-25 oC

18. Distribution of Coral Reefs Fig. 15-14

19. Coral Reefs • Conditions • Temperature • Too warm also problematic • Can cause bleaching and eventually death • Bleaching events often occur during periods of unusually warm water • Extreme low tide • El Niño event • Corals live near their upper thermal tolerance levels • Corals from warmer waters have higher thermal tolerance levels Fig. 15-33

20. Coral Reefs • Conditions • Salinity • Reefs tend to be absent or poorly developed near mouths of rivers • Sediments • Turbidity reduces light levels • Sediments can smother corals • Pollution • Corals sensitive to pesticides and other chemicals • Fertilizers support growth of algae that smother corals • Most corals grow in areas with low nutrient levels • Tidal Regime • Most corals intolerant of prolonged exposure