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Quite a diverse group Includes snails, slugs, clams, squids, and octopi Soft bodied animals Most have bilateral symmetry Usually have an internal or external shell secreted by a layer called the mantle Mantle – thin layer of tissue that covers most of the mollusks body Foot – contains feeding structures (may be flat for crawling, spade shaped for burrowing, or as tentacles for capturing prey) Shell – used for protection; composed of calcium carbonate Visceral Mass – internal organs Contain simple kidney-like organs to carry out excretion Gets rid of nitrogenous wastes (wastes from broken down proteins and cell parts) Aquatic mollusks breathe using gills Terrestrial mollusks breathe by diffusion through skin of the mantle cavity that is lined with blood vessels Have a digestive system with two openings: mouth and anus Feed in a variety of ways May have an open or closed circulation: Open Circulation – blood is pumped through Blood stays in vessels fromBlood heart dumpsto intoa saclike sinus. It then vessels and an open area and never comes passes through gills for gas exchange and surrounds the body in direct contact with finally backcells to heart. the body cells. Closed Circulation – blood is pumped around Open Closed the body by a heart but the blood remains Circulation Circulation inside blood vessels, similar to a human. Plan Plan Source Clams and other two shelled mollusks have a simple nervous system with a few nerve cords and sense organs Octopi and their relatives have the most highly developed nervous system of all invertebrates; they can actually learn and remember certain behaviors! Source Many snails and two-shelled mollusks reproduce utilizing external fertilization; large amounts of sperm and eggs are released into the water Certain snails and tentacled mollusks use internal fertilization Still others are hermaphrodites and fertilize eggs of another individual Based on characteristics of foot and shell Gastropods – pond snails, slugs, sea hares, etc. (shell-less or single shelled and move using muscular foot) Bivalves – clams, oysters, mussels, and scallops (have two shells held together by muscles) Cephalopods – octopi, squids, nautiluses, and cuttlefishes (soft-bodied, head is attached to foot which is divided into tentacles or arms) Source http://photos21.flickr.com/32523124_981521b b8a.jpg http://video.nationalgeographic.com/video/p layer/animals/invertebrates-animals/octopusandsquid/octopus_giant_kills_shark.html?source= G2101&kwid=shark|929542585