This burrowing urchin has relatively long, backward facing thin spines. It burrows in the sand with its spines facing backward. Usually buried by day, it plows around at or just under the surface of the sand, or crawls on algae at night. They can move pretty fast on the sand surface, especially when being chased by a predatory snail, Casmaria ponderosa, which is also common on the lagoon sand flats where these urchins are abundant.
Underside of the above specimen.
Created 16 June 2018