[4] Growing to a maximum diameter of 26 cm (10 in), Echinaster callosus has a small central disc and five slender cylindrical arms.

There are ambulacral grooves on the underside of the arms along which food is passed by ciliary action.

[4] E. callosus is found in the tropical and subtropical western Indo-Pacific, its range extending from East Africa and the Red Sea to Micronesia, and from Japan southwards to Australia and New Caledonia.

[4] The creeping comb jelly Coeloplana astericola sometimes live symbiotically on the aboral surface of this starfish,[5] as well as on the Luzon sea star, Echinaster luzonicus.

[6] Other associates are small worms and crustaceans, which do little harm, and the triton Charonia tritonis and the harlequin shrimp Hymenocera picta, which both feed destructively on its tissues.