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A siphon is an anatomical structure which is part of the body of aquatic molluscs in three classes: Gastropoda, Bivalvia and Cephalopoda. In other words, a siphon is found in some saltwater and freshwater snails, in some clams, and in octopus, squid and relatives. Siphons in molluscs are tube-like structures in which water flows (or more rarely in which air flows). The water flow is used for one or more purposes such as locomotion, feeding, respiration, and reproduction. The siphon is part of the mantle of the mollusc, and the water flow is directed to (or from) the mantle cavity. A single siphon occurs in some gastropods. In those bivalves which have siphons, the siphons are paired. In cephalopods, there is a single siphon or funnel which is known as a hyponome. ==In gastropods== In some (but not all) sea snails, marine gastropod molluscs, the animal has an anterior extension of the mantle called a siphon, or inhalant siphon, through which water is drawn into the mantle cavity and over the gill for respiration.〔Örstan A. 13 April 2007. (''Melongena's siphon'' ). Snail's Tales.〕 This siphon is a soft fleshy tube-like structure equipped with chemoreceptors which "smell" or "taste" the water, in order to hunt for food.〔Abbott, RT and Sandstrom, GF (2001) (''Seashells of North America'' ) Macmillan. ISBN 978-1-58238-125-1 Nassa mud snails, p. 142.〕〔(''Cone snails'' ). Hawaiian Marine Life. Accessed 18 November 2008.〕〔(''Respiratory system'' ). The apple snail website. Accessed 18 November 2008.〕 Marine gastropods that have a siphon are either predators or scavengers.〔(''Los Marineros Marine Life. Caption Mollusca''. ) Accessed 21 November 2008.〕 Although in gastropods the siphon functions perfectly well as a tube, it is not in fact a hollow organ, it is simply a flap of the mantle that is rolled into the shape of a tube.〔 In many marine gastropods where the siphon is particularly long, the structure of the shell has been modified in order to house and protect the soft tissue of the siphon. This shell modification is known as the siphonal canal. For a gastropod whose shell has an exceptionally long siphonal canal, see Venus comb murex. In the case of some other marine gastropod shells, such as the volute and the ''Nassarius'' pictured above, the shell has a simple "siphonal notch" at the anterior edge of the aperture instead of a long siphonal canal. The ''Aplysia'' gill and siphon withdrawal reflex is a defensive reflex which is found in sea hares of the genus ''Aplysia''; this reflex has been much studied in neuroscience. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Siphon (mollusc)」の詳細全文を読む スポンサード リンク
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