The adults are black in colour with a red ring around the outer edge of the mantle. There are up to 50 mm long. As juveniles they are reddish in colour, and get darker as they get older. The gill are black with white tips

Thsi north island species may extend as far south as Christchurch. It is found on rocky shores in the low tide zone.

It feeds on sponge.

Photo Credit: Rod Morris. Photos available from www.rodmorris.co.nz