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The sensory organs of bivalves are largely located on the posterior mantle margins. The organs are usually mechanoreceptors or chemoreceptors , in some cases located on short tentacles . The osphradium is a patch of sensory cells located below the posterior adductor muscle that may serve to taste the water or measure its turbidity .
The internal anatomy is visible, including the paired siphons to the right A siphon is an anatomical structure which is part of the body of aquatic molluscs in three classes : Gastropoda , Bivalvia and Cephalopoda (members of these classes include saltwater and freshwater snails , clams , octopus , squid and relatives).
The main body cavity is a hemocoel through which blood circulates; as such, their circulatory systems are mainly open. The "generalized" mollusc's feeding system consists of a rasping "tongue", the radula, and a complex digestive system in which exuded mucus and microscopic, muscle-powered "hairs" called cilia play various
Certain molluscs, such as the bivalves, [2] possess paired ctenidia, but others, such as members of the Ampullariidae, [3] bear a single ctenidium. [ 4 ] [ 5 ] A ctenidium is shaped like a comb or a feather, with a central part from which many filaments or plate-like structures protrude, lined up in a row.
In some mollusks the mantle cavity is a brood chamber, and in cephalopods and some bivalves such as scallops, it is a locomotory organ. The mantle is highly muscular. In cephalopods the contraction of the mantle is used to force water through a tubular siphon, the hyponome , and this propels the animal very rapidly through the water.
Because of the open circulatory system of gastropods and other molluscs, there is no clear distinction between the blood and the lymph, or interstitial fluid. As a result, the circulatory fluid is commonly referred to as haemolymph, rather than blood. The majority of gastropods have haemolymph containing the respiratory pigment haemocyanin.
The general structure of the veliger includes a shell that surrounds the visceral organs of the larva (e.g., digestive tract, much of the nervous system, excretory organs) and a ciliated velum that extends beyond the shell as a single or multi-lobed structure used for swimming and particulate food collection: veliger signifies "velum bearer ...
The hypobranchial gland is a glandular structure which is part of the anatomy of many mollusks, including several different families of gastropods, and also many protobranch bivalves. [1] This gland produces mucus as well as biologically active compounds. The cephalopod ink sac is a modified hypobranchial gland. [2]