This is heart-shaped urchin clothed in a dense mat of furrowed yellowish spines which grow from tubercles and mostly point backwards. The upper surface is flattened and there is an indentation near the front. This urchin is a fawn colour but the tests (skeletons) that are found on the strandline have often lost their spines and are white.

It buries itself in sand to a depth of ten to fifteen centimetres. It occurs in sediments with a wide range of grain sizes but prefers sediments with a size of 200 to 300 µm and a low mud content. It makes a respiratory channel leading to the surface and two sanitary channels behind itself, all lined by a mucus secretion. The location of burrows can be recognised by a conical depression on the surface in which detritus collects.

Organic debris is used by the buried animal as food and is passed down by means of the long tube feet found in the front of the ambulacrum (the groove along which the tube feet come out).

Broadcast spawner.

Collins: Gunson