As of October 2023 the accepted species are:[2] Marthasterias glacialis is a fairly large starfish with a small central disc and five slender, tapering arms.

Each arm has three longitudinal rows of conical, whitish spines, usually with purple tips, each surrounded by a wreath of pedicellariae.

The background colour is variable and may be brownish or greenish-grey, tinged with yellow or red and sometimes with purple at the tips of the arms.

[3] Like other starfish in the family Asteriidae, Marthasterias glacialis is a predator and feeds mostly on bivalve molluscs and other invertebrates.

[8] The reproductive biology of this starfish has been little studied but off the coast of Ireland, individuals gather together in very shallow water in July and August.