burrow into the sand with their foot Modifications of the mantle have provided them with two pegs of muscle for closing the shells, and with the muscular tube — the siphon or “neck” — that they extend to the sand surface and use to draw in passing food particles All the bivalves — clams, mussels, oysters — have comb-like gills for filtering food particles from the water that the mantle draws in and expels Mussels are also two-shelled filter feeders, but they attach their foot permanently to intertidal and subtidal rocks They have no need for a siphon, and one of their tough shell-closing muscles is much reduced Oysters cement themselves to inter- and sub-tidal rocks Their two heavy shells are closed by a single large muscle at their center, around which the mantle and other organs are organized The bulk of their body is the tender mantle and foodtrapping gills Scallops neither attach nor bury themselves They lie free on the ocean floor, and escape predators by swimming Their massive central muscle claps their shells shut and forces water out one end, thus propelling them in the other direction Squids and octopuses are molluscs turned inside out and transformed into highly mobile, streamlined carnivores with large eyes and arms The remnants of a shell provide an internal support, and the mantle is now a specialized muscular sheet that expands and contracts to provide jet propulsion through a small funnel derived from the foot muscle The immobile molluscs very well in aquaculture They can be raised in large numbers in the water’s three dimensions, ...their body is the tender mantle and foodtrapping gills Scallops neither attach nor bury themselves They lie free on the ocean floor, and escape predators by swimming Their massive central muscle... Their massive central muscle claps their shells shut and forces water out one end, thus propelling them in the other direction Squids and octopuses are molluscs turned inside out and transformed into highly... mobile, streamlined carnivores with large eyes and arms The remnants of a shell provide an internal support, and the mantle is now a specialized muscular sheet that expands and contracts to provide jet propulsion through a small