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Phylum Molluska. Over 50,000 species Coelomate , Protostomes , Bilaterally symmetrical Mostly marine, although some live in fresh water or land. Generally soft-bodied with a hard shell However, squid & octopi have internalized, reduced or lost their shells. Body Plan
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Phylum Molluska Over 50,000 species Coelomate, Protostomes, Bilaterally symmetrical Mostly marine, although some live in fresh water or land. Generally soft-bodied with a hard shell However, squid & octopi have internalized, reduced or lost their shells. Body Plan Although phenotypically diverse, mollusks share 3 common features A muscular foot - usually for movement A visceral mass - including internal organs A mantle - envelopes visceral mass and secretes a shell
Class Polyplacophora (chitons) • Marine animals - shells divided into 8 plates • Move using a muscular foot and graze using a scraping mouthpart called a radula
Class Bivalvia • Include clams, oysters and mussels • Have shells divided into 2 halves, connected by strong muscles • Has hatchet shaped foot for digging and anchoring • Are typically filter feeders drawing in water end expelling it through a siphon tube • Generally sessile, however, some species can quickly move by rapidly closing it's shell
Class Gastropoda • Include snails, abalone, and slugs • Largest class of mollusks ~40,000 species • Exhibit embryonic process of torsion • Visceral mass twists 1800 during development • Most species are herbivores, but some have modified radullas for boring into other mollusks • Some species have successfully colonized land
Class Cephalopoda • Unlike other mollusks, these are quick predators • Have beak-like jaws and poison to catch & immobilize prey • Beak is located @ the center of several long tentacles • Foot has been modified to form a siphon which allows most species to move quickly using a jet of water. • Only mollusks with a closed circulatory system (blood is always contained in vessels) • Very highly developed nervous system • Can learn complex behaviors • Octopi have learned to open jars to retrieve prey • May have rudimentary communication • Cuttlefish and octopi may communicate by skin coloration
