Shingle (or Helmet) Urchin, Colobocentrotus atratus

Pu'uhonua O Honaunau National Historical Park
The unusual, flattened spines of this species may help it to withstand the constant wave and tidal surges in its intertidal habitat.
(Phylum Echinodermata, Class Echinoidea, Order Echinoida, Family Echinometridae)