Siphonal canal
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In some sea snails, marine gastropod molluscs, the animal has an anterior extension of the mantle called a siphon, through which water is drawn into the mantle cavity and over the gill.
This siphon is a soft fleshy tube which also serves to "smell" or "taste" the water in order to locate a possible source of food.
In many (but by no means all) carnivorous snails, where the siphon is particularly long, the structure of the shell has been modified in order to house and protect the soft structure of the siphon. Thus the siphonal canal is a semitubular extension of the aperture of the shells of some marine gastropods, through which the siphon is extended when the animal is active.
One gastropod whose shell has an exceptionally long siphonal canal is the Venus comb murex. Some other gastropod shells have a simple "siphonal notch" at the edge of the aperture instead of a siphonal canal.
