Cantharidus roseus is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails.
Cantharidus roseus Wikipedia
The length of the shell varies between 4 mm and 12 mm. It grazes on kelp. The small, imperforate, thin, fragile shell has a globosely conoidal shape. Its sculpture consists of very finely spirally striated, with 30 striations on the penultimate whorl and obscured on the body whorl by growth lines. The colour is variable and typical. The 2 apical whorls are white or pinkish-white, on the third whorl 2 purplish bands equidistant from the sutures arise. The 4th whorl is wholly purplish-black, as is the body whorl. In some shells these bands persist on to the last 2 whorls. Additional bands arise so that on the body whorl 5 distinct bands can be counted. Rarely additional minute bands can be seen between these principal bands. In some cases the purple on the last whorl breaks up into irregular dashes. The shells found at ShagPoint are mostly light-coloured. Some have almost a white ground colour, with 5 separate distant bands. Others have a pinkish ground colour, with darker markings between the principal bands. Whilst in some the bands on the body whorl are broken up into dots.
The spire is very short. and contains five whorls. The body whorl is very large, rapidly descending. The suture is distinctly marked. The aperture is large and round. The outer lip is thin, edged with a thin band of white, inside iridescent. The columella is subvertical, semicurved, expanding as a callus over the umbilicus.
This marine species is endemic to New Zealand and occurs off South Island, Otago to Stewart Island, and Snares Islands.