Siphon (mollusc)

Sipho (plural: siphons), siphe (Gr. siphon "tube", "splash", "siphon") or siphon is the name given to a tubular organ in various groups of shell molluscs (Conchifera). It fulfils various functions, mostly in connection with the supply of oxygen-rich fresh water to the ­shell and/or the removal of excrement-laden ­old water from the shell.

• In cephalopods (Cephalopoda), it is a strand of tissue traversed by blood vessels and surrounded by a porous, partly calcareous, partly chitinous sheath (siphonal sheath). Starting from the visceral sac in the living chamber, it extends backwards through all the housing chambers - known in their entirety as the phragmocone - to the initial chamber. Via the sipho, an aqueous liquid can be osmotically released into or taken up from the youngest chamber(s) and, in turn, an air-like gas mixture can be taken up or released by passive diffusion. This serves to regulate the buoyancy of the enclosure. Sipho and phragmocone thus together form a hydrostatic apparatus.
• In some aquatic snails (Gastropoda), the sipho is an extension of the mantle margin for the introduction of respiratory water into the gill chamber of the shell.
• In bivalves (Bivalvia), there are two openings (respiratory and anal sipho) at the posterior edge of the mantle, which are fused together and extended to form a tube.

In insects, a siphon is a breathing tube used underwater as a snorkel.

See also

• Siphon (disambiguation)
• Sipho (aphids)