Unit 8 Chapter 27 Mollusks and Segmented Worms

What is a Mollusk? Bilateraly symmetry, coelomates, and well-developed body systems Soft bodies covered by a thin mantle, which may secrete a shell

What is a Mollusk? Mollusks have a foot, a ventral structure for locomotion Some have an open circulatory system, blood moves through vessels & into open spaces around body organs Others have a closed circulatory system, blood moves through the body enclosed entirely in blood vessels

What is a Mollusk? Gastropods include snails and slugs One shell, “belly- footed” Radula = scraping tongue-like structure Radula magnified 1000X

What is a Mollusk? Bivalves include clams, oysters & muscles Two shells, “hatchet-footed” Filter-feeders

What is a Mollusk? Cephalopods include octopus, squid, cuttlefish, & chambered nautilus Little or no shell, foot divided into tentacles with suckers Use ink and jet propulsion to escape from danger

What is a segmented worm? Phylum Annelida Bilaterally symmetrical, segmented coelomates, with two body openings

What is a segmented worm? Earthworms have complex body systems: Digestive system includes a crop & gizzard for grinding food taken from soil Closed circulatory system includes 5 pair of “hearts” Reproductive system includes both ovaries & testes

What is a segmented worm? Leeches are freshwater, external parasites Some microsurgeons use leeches after surgery to improve blood flow

What is a segmented worm? Marine worms include bristle worms, fan worms and tube worms (below) Most have structures for swimming or crawling on the bottom of the sea