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Worms & Mollusks. Chapter 27. Flatworms. Phylum Platyhelminthes Bilateral symmetry All 3 germ layers Cephalization One digestive opening Acoelomate. 3 groups of flatworms. 1)turbellarians Class Turbellaria 2)flukes Class Trematoda 3)tapeworms Class Cestoda. turbellarians.
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Worms & Mollusks Chapter 27
Flatworms Phylum Platyhelminthes Bilateral symmetry All 3 germ layers Cephalization One digestive opening Acoelomate
3 groups of flatworms • 1)turbellarians • 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 • 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
http://www.youtube.com/watch?v=7ujRgSRYE9A • http://www.youtube.com/watch?v=1rDsK9qxxAk&feature=related