O.F. Müller, 1776
Purple Heart Urchin
Test broad, rather low, regularly arched on the upper side, flat on the under side. Reaches a considerable size, up to 120 mm. Colour violet, the long curved spines of the upper side lighter. The colour does not fade in alcohol.
Ambulacra on upper side of test petaloid, widened, scarcely deepened. Frontal ambulacrum rather deep, forming a conspicuous broad notch in anterior edge of the test. First plate of posterior interambulacrum developed into a prominent lip, partly covering the mouth and the transversely elongated peristome. Mouth anterior, anal opening posterior. The mouth is not much sunken. A dental apparatus is lacking. Test with only a closed subanal fasciole, about three times as broad as long. There are no gills or gill-cuts at peristomial edge of the test. Sphaeridia present, not in grooves. Tube-feet confined to the ambulacra.
Spines of various length, those on the posterior interambulacrum (plastron) often widened into "S" spade-shape. Small, close-set, spines form the subanal fasciole. Fairly numerous large spines in the interambulacra outside the petaloid part.
Pedicellariae very conspicuous, besides the usual four types (triphyllous, globiferous, ophicephalous and tridentate pedicellariae), also a fifth form: the rostrate pedicellariae
It prefers a rather coarse sand or gravel bottom, in which it lies wholly buried. It is found from the lowermost tide limit down to ca. 900 m.
The species is common in the whole North Sea. Elsewhere it is distributed from North Cape to the Azores and the Mediterranean, but is not found at Greenland or the Atlantic coast of N. America.