A modest urchin of silty sand and seagrass, up to about 8 cm (3 in) across, with short even spines in greenish or reddish brown. The character that names it is on the shell itself: the test is deeply grooved and pitted between the spine bases, a sculpted surface that shows clearly on empty tests washed up on the beach.
It lives away from coral, on soft bottoms where it ploughs slowly through the top layer of sediment and takes detritus and diatoms, often with a covering of shell fragments and weed held over itself with the tube feet. That habit - carrying debris as a sunshade and a disguise - is shared with several urchins of open ground and makes them easy to overlook entirely. Spines are short and harmless. Empty tests are common finds and are worth a look for the sculpture, which is more striking than the living animal.
- short even spines, greenish to reddish brown
- test visibly grooved and pitted between the spine bases
- on silty sand and seagrass rather than on reef
- diameter up to 8 cm
