The seagrass sea star, dark cones on top and commensal shrimps underneath.
A heavy five-armed sea star to about 30 cm across, the arms short and broad and the whole animal stiff rather than flexible. The upper surface is cream, tan or red-brown and carries a row of large dark conical tubercles down the middle of each arm and a ring of them around the disc, joined by a raised network of ridges, which is where both the horned and the chocolate chip names come from. The number and height of the cones varies from one animal to the next and is not a species character. It is not confused with much: Culcita novaeguineae is a pentagonal cushion with no free arms, and Linckia laevigata is blue with long cylindrical arms and no tubercles.
Its habitat is shallow sand and seagrass rather than reef, and it is found in aggregations there, sometimes in large numbers on a single meadow, grazing the microbial film, detritus and small invertebrates on and just under the surface. It is one of the more productive sea stars to turn over — figuratively, since lifting one out of the water damages it. The sea star shrimp Zenopontonia soror sits on the oral surface in the ambulacral groove or beside the mouth, coloured to match the host, often as a pair; small brittle stars and worms use the same space. The species is collected in quantity for the dried curio trade, and the shallow accessible meadows it prefers are the ones nearest to that pressure.
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.