Features Gastropod shells are mostly made up of aragonite. Most shells are asymmetrically coiled. Shells have simple structure with apex and aperture at the two ends. The shell is divided into whorls separated by suture . The last whorl which is usually the largest is the body whorl .
Most gastropods have large aperture through which the organism comes out.
There are three major orders of gastropods - Prosobranchiata, Opisthobranchiata and Pulmonata. Prosobranchiata Prosobranchiata includes the oldest gastropods, archaeogastropod, which coil in one plane and bellerophontids which coil symmetrically in one plane. Others are asymmetrically coiled. Their fossil records start from the Cambrian and are abundunt in the Palaeozoic . They are at the climax of their development now.