A sea star that has stopped looking like one: a swollen pentagonal cushion up to 30 cm (12 in) across with no arms to speak of, its surface studded with short blunt spines and tubercles, mottled brown, orange or greenish. The five-part symmetry is still there in the outline, but the animal reads more as a stray pillow on the sand than as a relative of the starfish beside it.
It lives on sand and rubble among coral heads from about 1 m to 30 m (3 to 100 ft), grazing algal film, detritus and small encrusting animals, and taking live coral polyps as well. Juveniles look nothing like this - they are flat, plated and genuinely star-shaped, and were long described as a separate genus before anyone connected them to the adult. Small commensal shrimp and juvenile pearlfish sometimes shelter beneath the underside, so a careful look at a cushion star lying on sand can turn up a second animal. The spines are blunt and harmless to a diver.
- pentagonal cushion with no visible arms
- surface covered in short blunt spines and tubercles
- mottled brown, orange or greenish
- diameter up to 30 cm
