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Phylum Mollusca

Phylum Mollusca. Phylum Mollusca One of the oldest and most diverse phyla Second largest phyla of animals Soft-bodied animals with an internal or external shell Have a free swimming larval stage. 27-4 Mollusks. Body Plan. True coelomates

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Phylum Mollusca

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  1. PhylumMollusca

  2. Phylum Mollusca One of the oldest and most diverse phyla Second largest phyla of animals Soft-bodied animals with an internal or external shell Have a free swimming larval stage 27-4 Mollusks

  3. Body Plan • True coelomates • Complex, interrelated organ systems function together • 4 parts: foot, mantle, shell, visceral mass • Foot: used for crawling, burrowing, tentacles • Mantle: thin layer of tissue that covers most of the body • Shell: made by glands in mantle that secrete calcium carbonate (reduced or lost in some) • Visceral Mass- beneath mantle, consists of internal organs

  4. Feeding • Herbivores, carnivores, detritovores, parasites • Radula- flexible, tongue-shaped, rough structure • Used to scrape algae or eat soft tissues • Filter feeders- clams, oysters, scallops- siphon water • Siphon- tubelike structure for water to enter and exit

  5. Respiration, Circulation, Excretion • Gills in the mantle cavity- snails, clams and octopi • Through mantle blood vessels- land snails and slugs • Open circulatory system- snails, clam- slow because low oxygen demand • Closed circulatory system- octopi, squid- transports blood quickly • Cells release waste into blood and nephridia remove ammonia from the cell

  6. Response and Movement • Bivalves- burrow- simple nervous system • Chemical receptors, eye spots • Octopi- most highly developed nervous system in all invertebrates • Good memory, complex behavior • Snails move using mucus secreted along the base of the foot • Octopi and squid move using jet propulsion

  7. Reproduction • Sexually • External fertilization: sea snails and bivalves • Internal fertilization • Tentacled and some snails • Some are hermaphrodites - nudibranchs • Not self fertilizing

  8. Class Gastropoda • Pond snails, land slugs, sea hares, limpets and nudibranch • “Stomach-foot” • Single-shelled- protected by withdrawing and covering the opening with an operculum • Snails • No external shell- protected by hiding, ink squirting, poison, bright colors, nematocysts • Slugs, nudibranchs, and sea hares

  9. Nudibranch

  10. Class Bivalvia • Have two shells that are held together by one or two powerful muscles • Clams, mussels, oysters, scallops • Stay in one place, dig or burrow or attach • Scallops flap shells when threatened • Cilia or gills create current to circulate water

  11. Class Cephalopoda • Octopi, squid, cuttlefish, chambered nautilus • “Head-foot” • Most active of the mollusks • Soft-bodied head attached to foot (tentacles) • Tentacles have sucking disks and grab hold of prey • Most have an internal shell- except nautilus • Complex eyes- can distinguish shapes by sight and texture by touch

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