The heart urchin ties into Mollusca.
In Hawaii, the favorite food of Cassis cornuta is the heart urchin,
which my ancient book "Reef and Shore Fauna of Hawaii" by Charles Howard
Edmondson published by Bishop Museum Special Publication 22, 1946
gives the name Brissus latecarinatus (Leske), in family Spatangidae.
Aloha,
Wes