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DescriptionVelutina velutina can be up to 1 cm long by 1 cm wide. The shell is white to pinkish in colour but covered by a thick dark brown periostracum. The shell is tumid in shape, with 2-3 whorls that expand rapidly so that the last whorl occupies the whole shell height, and its nearly circular aperture occupies 90% of the last whorl. The spire is low, occasionally in a small depression. The shell is fragile and semi-transparent, with fine spiral and growth lines, obscured by the periostracum. There is no operculum, and the small mantle flaps enable the whole of the animal to be drawn into the shell. The flesh is white or yellowish, with the smooth and greatly thickened mantle edge having many white points. The foot has a shield-like appearance with double-edged anterior margin.This is a northern hemisphere species that feeds on solitary ascidians such as Styela and large hydroids (e.g. species of Tubularia). Breeding occurs in the spring. The larva of the species has a flat discoidal, soft and gelatinous shell that lacks marginal keels, and becomes bloated in latter stages of development.