Portlock, Oahu, 1 foot, 20 mm

Diamond Head, Oahu

Fairly common under rocks in shallow water where it preys upon vermetid snails.  The black spines are not aligned into axial ribs, and the aperture is purple.  Most are heavily encrusted with coralline algae.  Attains 1.3 inches, 30 mm.  Red Sea to Hawaii and Pitcairn.