Siphonal notch

A shell ofAcus crenulata,with the siphonal notch visible near the bottom left of the image, at the anterior end of the shell.

A live individual of thevolutespeciesCymbiola magnificashowing thesiphonextended through the siphonal notch of the shell

Asiphonal notchis a feature of theshellanatomy in somesea snails,marinegastropodmollusks.

In these particular groups of sea snails the animal has a soft tubularanteriorextension of themantlecalled asiphonthrough which water is drawn into themantle cavityand over thegilland which serves as achemoreceptorto locate food. This siphonal opening also serves for the exit of the water that has entered by the branchial opening.

The siphonal notch is a noticeable notch situated at the most posterior part of theapertureof the shell, through which the siphon is extended when the animal is active. The notch at the posterior end of the aperture is also called the anal notch, anal sinus, anal canal or posterior canal.

Instead of a simple siphonal notch, some gastropods have an elongatedsiphonal canal,a hard shell tube which extends out from the anterior edge of the aperture.

See also

• Siphonal canal
• Stromboid notch