[1] The genus name was given by Walter Kenrick Fisher to honor the American biologist and administrator Richard Rathbun of the Smithsonian Institution.

The only species in the genus, Rathbunaster californicus,[2] common name California sun star, has a maximum size of about 45 centimeters in diameter[3] and an average weight of 35 g. It lives on muddy benthic substrates between 60 and 1,000 m below the surface.

[3] Original description:[5] It resembles closely Pycnopodia Stimpson, but differing in having a smaller disk, with the rays constricted at the base and easily detachable.

In the entire absence of rudimentary annular or calcareous ridges at the base of the ray, in the abortion of alternate supermarginal plates beyond the base of the ray, and in the small widely spaced inferomarginals each bearing a slender spine; in the greater prominence of the adambulacral plates which are placed on the same level with the inferomarginals (and each with a single spine as in Pycnopodia); in the less crowded condition of the ambulacral ossicles.

[8][failed verification] The endoskeleton of R. californicus is made up of calcareous ossicles, which are covered in a thin layer of the ciliated tissue.

[8] Rathbunaster californicus is a carnivore and detritivore, feeding on crustaceans, worms, detritus, and fish using pincers on its aboral side.

It plays multiple important ecological roles, eating a variety of organisms and controlling populations of those species.

[4] In Monterey Canyon, R. californicus has been found infected with an endoparasitic gastropod called Asterophila rathbunasteriWaren & Lewis, 1994.