Young Culcita are unremarkable asteroids: flat, with five distinct arms and the usual radial outline. Growth is disproportionate. The interradial areas expand faster than the arms, the body wall thickens and the interior fills, so the arms are progressively swallowed by the widening disc. Large adults show only five shallow corners.
The change was pronounced enough that juveniles and adults were at times treated as separate taxa. The adult retains the standard echinoderm anatomy underneath, including tube feet in ambulacral grooves along the underside and the everting stomach used to feed on coral and encrusting organisms.
The cushion form also creates habitat. Commensal shrimp of the genus Periclimenes live on the surface, and the pearlfish Carapus is recorded sheltering inside cushion stars as well as sea cucumbers. Whether the cushion shape evolved primarily as predator defence, as a feeding-surface increase, or as a consequence of internal volume demands is not clearly resolved.