A small pencil urchin with a handful of thick, blunt spines banded light and dark, the whole animal rarely more than 4 cm (1.6 in) across. Unlike the fragile needles of a Diadema these spines are solid rods, and they are frequently overgrown with algae, sponge and encrusting animals until the urchin looks like a piece of debris with legs.
That overgrowth is not accidental: pencil urchins do not shed their spine surface the way other urchins do, so anything that settles there stays. It wedges itself into crevices and under rubble by day and grazes at night on algae, sponge and small encrusting animals. The spines are harmless to handle - blunt, solid and without venom - which makes this one of the few urchins on the reef a diver can touch safely, though there is no reason to.
- few thick blunt spines, banded light and dark
- spines often overgrown with algae and encrusting life
- small test, rarely over 4 cm
- wedged in crevices, rarely in the open
