The aboral (upper) surface is slightly convex and is covered in paxillae, umbrella-shaped structures with spiny margins.

The madreporite is about halfway from the centre of the disc to the margin, the anus is small, and there are respiratory structures known as papulae between and concealed by the paxillae.

A notable feature are the 13 to 20 large calcareous plates, wider than they are long, that extend around the margins of each arm.

[3] Trophodiscus almus was thought to be endemic to the Sea of Okhotsk from where it was first described by the American zoologist Walter K. Fisher in 1917 from material collected by the marine research vessel USS Albatross (1882).

Brooding the young in this location is very unusual among starfish, and the only other species known to do it are the sister species, Trophodiscus uber, from the Sea of Okhotsk, Leptychaster kerguelenensis from the extreme south of the Indian Ocean and Ctenodiscus australis from the Southern Ocean.