Worms & Mollusks Chapter 27

Flatworms Phylum Platyhelminthes Bilateral symmetry All 3 germ layers Cephalization One digestive opening Acoelomate

3 groups of flatworms 1)turbellarians 2)flukes 3)tapeworms Class Turbellaria 2)flukes Class Trematoda 3)tapeworms Class Cestoda

turbellarians Free living

Flukes Parasitic Live in internal organs

tapeworms intestinal parasites of vertebrates, where they absorb predigested nutrients (they have no digestive tract).

Roundworms Phylum Nematoda Bilateral symmetry All 3 germ layers Cephalization 2 digestive openings Pseudocoelomate Most are parasitic

Roundworms & Disease Trichinosis (from undercooked pork) Filarial worms (elephantiasis)

Ascarid worms (intestine parasites) Hookworms (25% of world population)

Segmented worms segmented Phylum Annelida Bilateral symmetry All 3 germ layers Cephalization 2 digestive openings Coelomate segmented

Classes Oligochaeta earthworm Polychaeta many bristled worms Hirudinea leeches

Mollusks Phylum Mollusca Soft bodied invertebrates that usually have an internal or external shell. Bilateral symmetry All 3 germ layers Coelomates Cephalization 2 digestive openings “open” circulatory system

Groups of Mollusks 1)Gastropods: (class Gastropoda) snails, slugs, limpets, nudibranchs Move using a muscular “foot”

2)bivalves: (class Bivalvia) clams, mussels, oysters, scallops Have 2 shells held together by powerful muscles.

3)cephalopods: (class Cephalpoda) octopus, squid, cuttlefish, nautilus Soft bodied mollusk with head atteched to foot. Foot is divided into tentacles Most intelligent invertebrates

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