The anal sulcus, also called the anal sinus or anal canal, in
Gastropods
The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda ().
This class comprises snails and slugs from saltwater, from freshwater, and from land. The ...
is a notch, a shelly tube at the top of the
aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane.
An ...
.
It is the first notch close to the
suture. It houses the anal siphon through which the snail expels water and waste products.
![Drillia poecila 001](https://upload.wikimedia.org/wikipedia/commons/1/10/Drillia_poecila_001.jpg)
The anal sulcus can be described, according to the species, as well-defined, weakly defined, shallow, sharp, wide, narrow or inverted U-shaped. In some species, such as in the
Murex family, the anal sulcus is absent.
The anal sulcus can be linked on the edges to a fasciole, a spiral band on the shell, formed by successive growth lines. It can also have a subsutural callus (such as in
Clathrodrillia callianira).
References
Gastropod anatomy
Mollusc shells
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