The
siphonal canal is an anatomical feature of the
shells of certain groups of
sea snails within the clade
Neogastropoda. Some sea
marine gastropods have a soft tubular
anterior extension of the
mantle called a
siphon through which water is drawn into the
mantle cavity and over the
gill and which serves as a
chemoreceptor to locate food. In certain groups of
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 semi-tubular extension of the
aperture of the shell through which the siphon is extended when the animal is active.