Bright cobalt, common in the shallows, and it can regrow a whole body from one arm.
A five-armed sea star to about 30 cm across, the arms long, cylindrical and blunt-tipped, and the colour an even bright cobalt blue — occasionally aqua, pale green or, rarely, pink or orange. The pigment is unusual among sea stars and its function is not settled. The surface is granular and firm.
It sheds arms readily, and a detached arm can regenerate an entire animal from itself; a star with one long arm and four short regenerating ones — a “comet” — is a common sight and is one individual rebuilding, not five. Grazes on the microbial film and detritus on hard surfaces. Like most large sea stars it carries associates: the parasitic snail Thyca crystallina is often stuck to an arm as a small blue-white lump, and the shrimp Zenopontonia soror rides on some individuals. Recorded from the intertidal to about 25 m. Lifting one out of the water damages it, which is worth knowing given how often it is picked up.
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.