Viviparus viviparus
Viviparus viviparus is a species of large freshwater snail with a gill and an operculum, an aquatic gastropod mollusk in the family Viviparidae, the river snails. This species is a viviparous (ovoviviparous) snail. Description The height of the shell is 25–35 mm. The width of the shell is 20–26 mm. Males are 2 mm smaller than females of the same age. The shell colour is dark greenish brown or greyish yellow, with three reddish brown spiral bands. The shell is striated but has no hammer pattern. The shell apex is blunt (more pointed in other Viviparus species). The shell has 5.5-6 weakly convex whorls. The last whorl is relatively large compared to that of other Viviparus species. The umbilicus is narrow. The animal can lock itself in behind a round lid which shows concentric striations (the operculum). This allows it to protect itself from dehydration, for several months if necessary. Once closed the operculum is flush with the opening of the shell. The operculum is attached to the dorsal surface of the rear of the foot of this gastropod, the body of which is wide and T-shaped, and the colour of which varies from spotted grey to greenish to orange.