Pteraster militaris

Lore & Background

Pteraster militaris is a robust starfish with a wide disc, a large central pore, and five short, wrinkled, triangular arms. Its aboral surface is dotted with papulae, each topped with four short spines, and covered by a papery covering that gives it an inflated, bulky appearance. It grows to a diameter of 85 millimeters and is usually orange, pale yellow, or white, sometimes with red tips to its arms.

This species is found in rocky habitats in waters down to 1,100 meters deep across the northern Pacific Ocean, the Arctic Ocean, the Barents Sea, and the northern Atlantic Ocean. It feeds on various species of sponge, including the cloud sponge (Aphrocallistes vastus) and the white reticulated sponge (Iophon cheliferum), as well as hydrozoans such as the pink branching hydrocoral (Stylaster norvigicus) and the purple encrusting hydrocoral (Stylantheca).

Pteraster militaris is unusual among starfishes in that it broods some of its young. About forty fertilized eggs are retained in the water-filled chamber below its papery outer skin, where they develop into juveniles that may reach 1 cm across before exiting through the central pore. Eggs too numerous to be brooded are released directly into the sea as planktonic larvae. The brooded juveniles appear to behave as ectoparasites of the female, feeding on maternal tissues, dead embryos, fecal material, and mucus.

Reader's Guide

Pteraster militaris holds significance in marine biology primarily for its distinctive reproductive behavior, which is rare among starfishes. The species broods about forty fertilized eggs in a chamber beneath its papery outer skin, where juveniles develop to about 1 cm before emerging through the central pore. This brooding strategy contrasts with the release of excess eggs as planktonic larvae, illustrating a dual reproductive approach. The brooded juveniles act as ectoparasites, consuming maternal tissues, dead embryos, fecal material, and mucus, a behavior that highlights an unusual parent-offspring dynamic. Ecologically, the wrinkled star occupies rocky habitats across a broad depth range in cold northern waters, from the Arctic to the northern Pacific and Atlantic Oceans. Its diet includes sponges and hydrocorals, linking it to benthic food webs. The species' physical traits—a wide disc, short wrinkled arms, and a papery covering with papulae—distinguish it visually. Its legacy lies in providing a clear example of brooding and ectoparasitic development in echinoderms, contributing to the understanding of reproductive diversity among starfish.

Did You Know?

• Pteraster militaris broods about forty fertilized eggs in a water-filled chamber under its papery outer skin.
• It feeds on sponges such as the cloud sponge (Aphrocallistes vastus) and hydrocorals like the pink branching hydrocoral (Stylaster norvigicus).