The animal is about 4 cm in diameter. The shell tube is closed by a brown proteinaceous operculum. There are three major, and many minor grades of snail structural organization. Within such a grade of structure, the animals share some common attributes. Although grades of structure often have groups of closely related animals in them, kinship is not implied by the structural similarity.
Many groups look alike and have similar structures due to convergent evolution.
In effect they get to about the same endpoint, but by different pathways, and from different origins. This individual was about 3 m from the individual photographed in the previous figure, and is the same species. It is feeding and the feeding mucus is visible coming from the aperture. These are the snails that have shells similar to the earliest snails in the fossil record. Presumably their soft parts are similar, too, however that is not certain as the soft parts don't fossilize while the shells do.