The ragfish, Icosteus aenigmaticus, is a ray-finned fish of the northern Pacific Ocean; although a perciform, its skeleton is mostly cartilage, and the larvae have pelvic fins that disappear as they mature. It is the sole member of the family Icosteidae, and some authorities place it into its own order Icosteiformes. The larvae make a remarkable transformation as they mature; the dorsal fin and anal_fin both shrink, and the pelvic fins disappear. Formerly, adult ragfishes were considered to be a different species, known then as Acrotus willoughbyi.