the opening of the shell through which the animal can expand (never used for the mouth in the soft parts).
In the Limacinidae and Clioinae the aperture is rounded or triangular and continuous (see A in figure of Thecosomata below).
In the remaining Cavoliniidae the aperture is composed of the main central part (see figures of Diacavolinia longirostris & Cavolinia t. teschi) and two lateral slits (see fig. Cavolinia t. teschi).
The height of the aperture is equal to the maximum height of the shell aperture, in straight ventral view or oral view.
See also: Aperture sinus

Alternative forms for aperture : apertural, apertures, shell aperture, shell apertures.