E-Fauna BC: Electronic Atlas of the Wildlife of British Columbia

Hippasteria spinosa is spiny, vermilion and star-shaped with five arms up to 17 cm long. The oral surface is usually a lighter orange to white. The ratio of arm to disc ranges from 1.7 to 2.6. The aboral surface has large plates, each bearing a single stout tapering spine; secondary plates are interspersed, some with a conspicuous bivalve pedicellaria, the jaws of which are slightly wider than their height. These pedicellariae are variable and may resemble the H. californica type, which are taller and narrower. All plates are surrounded by granules, giving them a star-shaped appearance. H. spinosa has 16 or 17 superomarginals, each surrounded by a row of smooth granules and bearing two stout spines, reducing to one at arm tip; the inferomarginals are similar. The oral intermediates are oval and surrounded by pointed granules bearing stubby spinelets or low bivalve pedicellariae. The adambulacrals have two or three furrow spines and a single stout spine on the oral surface of the plate, surrounded by granules or spinelets. The mouth plates have four or five marginal spines.

Flat body. Prominent marginals; the supero- and inferomarginals are similar. The aboral plates are flat or paxilliform, bearing granules, low stumps or spines. Only the radial areas have papulae. Pedicellariae are generally present. The tube feet have suckers.

Hippasteria spinosa should not be confused with any other species in this book. Its closest relative is H. californica from deeper water.