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Mollusks Marine Biology Lindsey Maddox and Davis Carberry Phylum: Mollusca Inside the Phylum Mollusca there are 9 different Classes. Aplacophora, Bivalvia, Cephalopoda, Polyplacophora, Gastropoda, Monoplacophora, Pleistomollusca, Rostroconchia, and Scaphopoda. Bivalvia One body in a shell with two hinged parts. Clams, oysters, mussels, scallops are just a few examples of animals in this class. Filter feeders that have no head. Gills have evolved into ctenidia. Specialized organs for breathing and feeding. Attach themselves to rocks or any other hard surfaces. 3 part nervous system (mouth, digestive system, and foot) 500 million years old Cephalopoda Advanced nervous system- lobes with nerve cells, sensory system Head and foot specialized for free swimming Predators Circles of tentacles from the head Beak Closed circulatory system- rapid movement of materials Separate sexes Egg into juvenile without trochapore larvae Chromatosphores Cephalopoda cont. Squid/Cuttlefish- 8 tentacles 2 arms, internal shells Octopus- 8 tentacles Onambered Nautiluses- retains external shell, coiled & divided into series of gas filled chambers, soft body moves as the organisms grow, and bouyant Gastropoda Largest and most diverse group Single shell Torision- larval deve. V.M. twists 180 in relation to the head Brings anus, gills, and mantle cavity in the front, allows adult to pull itself into the cavity when threatened Move by wave like motion of foot, open circulatory system- Hemolymph- flows into hemocoel (blood cavity) Separate sexes but may be hermaphroditic Citations www.wikipedia.com Marine Science textbook