Body whorl

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The body whorl in a mollusc shell is the most recently formed whorl of a spiral shell, terminating in the aperture. The size of the body whorl differs greatly according to shell morphology. In shells in which the rate of whorl expansion after each revolution around the axis is very high, the aperture, and hence the body whorl, is large, and the shell tends to be low spired. The abalone is a good example of this kind of shell. The opposite tendency has a high spire and very little whorl increase per revolution. In these instances, e.g. the Turritella, both the body whorl and the aperture is relatively small. In mollusc shells where there is little or no spire, but only slight whorl expansion, the body whorl may still be large and encompass a large part of the shell, e.g. the Nautilus or Planorbis.