"echinaster spinulosus" is a medium sized sea star with five long tapering arms, round in cross section, attached to a central disc. near one edge of this is the madreporite, a structure used for drawing in water to replenishing the water vascular system. the aboral or upper surface is covered in flat plates, each of which bears several short, blunt spines. these plates are quite prominent. they have fine granulations and are arranged in fifteen to twenty irregular rows that continue down the arms. on the margin of the arms are a row of plates with flattened spines and on the oral (under) surface, on either side of the ambulacral grooves, are larger plates, each bearing one small and two larger spines. in the grooves there are several rows of bright orange tube feet with suckers. the tips of the arms bear tiny orange eye spots and are often turned upwards. this sea star grows to about in diameter and its general colour is maroon or brown flecked with white. the body wall of the disc and arms is composed of collagen fibres arranged in a three-dimensional web with calcareous plates in between. this arrangement provides a protective surface with flexibility when the sea star moves around and rigidity when required.