In
gastropods, the body whorl, or last whorl, is the last or final complete coil of the shell, measured from the
aperture back to where the last half-turn began. The body whorl encompasses the entire volume of the final coil and terminates at the aperture and its margins (peristome), which are an integral part of the body whorl structure. It is called the "body whorl" because most of the body of the soft parts of the animal fits into this whorl. The proportional size of the body whorl in gastropod shells differs greatly according to the actual shell morphology. For shells in which the rate of whorl expansion of each revolution around the axis is very high, the aperture and the body whorl are large, and the shell tends to be low
spired. The shell of the
abalone is a good example of this kind of shell. The opposite tendency can sometimes create a high spire with very little whorl increase per revolution. In these instances, e.g. in the shell of
Turritella species, both the body whorl and the aperture are relatively small. In mollusc shells where there is no elevation at all to the spire, and only moderate whorl expansion, the body whorl can sometimes still represent a large part of the shell, e.g. in some species in the family
Planorbidae, such as the genus
Segmentina. == In cephalopods ==