A burrowing urchin under a coat of fine spines, most often met as a bare test on the sand.
An irregular echinoid, oval to heart-shaped in outline and flattened underneath, to about 8 cm long, covered in short fine spines that lie back along the body and look more like fur than like the armament of a regular urchin. The mouth is set forward on the underside rather than centrally and there is no chewing apparatus. Colour in life is grey-brown to fawn.
The bare test is what most divers see, and it is worth recognising: a thin white or pale shell, fragile, marked on top with a five-part petal pattern of paired pore rows, and often lying in numbers where current has gathered them. Live animals are under the sand, ploughing horizontally a few centimetres down and taking organic material from the sediment as they go, and the sign of one is a shallow depression with a raised trail of disturbed sand behind it.
They come up onto the surface occasionally, mostly at night, and are then out in the open on soft ground with the spines flat and a fine film of sediment held over the body. The group is diverse and the species are separated on the arrangement of the plates and pore rows, so a record from a dive normally stays at the order. Recorded from about 3 to 35 m on sand and silt.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.