The pin cushion sea star is a large sea star with a very distinctive appearance. Its thick, domed body has five very short arms that are barely distinguishable from the broad central disc, giving it an overall cushion-like or rounded pentagonal shape.

Its surface is relatively smooth, and its coloration is highly variable, although it is often red, sometimes with darker or differently colored spots on the body. It may also display orange, yellow, brown, gray, greenish, pink, or purplish shades.

The pin cushion sea star can reach up to 12 inches in diameter.

The pin cushion sea star inhabits coral reefs as well as seagrass beds in shallow waters. It can particularly be observed on reef flats where seagrasses and algae grow.

The pin cushion sea star feeds on algae and small organisms found on the seafloor. It can also consume corals by everting its stomach over their surface to digest their tissues.

The pin cushion sea star reproduces sexually, with separate male and female individuals. The gametes are released into seawater, where external fertilization takes place. The eggs then develop into larvae that spend some time in the plankton before undergoing metamorphosis and settling on the seafloor to continue their development.