Sebastolobus

Sebastolobus, known as thornyheads, is a genus of marine ray-finned fish in the rockfish subfamily Sebastinae, part of the Scorpaenidae family. These fish live in deep waters across the northern and eastern Pacific Ocean.

The genus was established in 1881 by American ichthyologist Theodore Gill. Its type species, Sebastes macrochir, was originally described in 1877 by Albert Günther, with a type locality of Japan. The name Sebastolobus combines Sebastes (the original genus) with lobus, meaning "lobed," referring to the lower pectoral fin rays being widened into tongue-shaped lobes. This genus is the type for the tribe Sebastolobini, one of two tribes within Sebastinae.

Three species are currently recognized. Thornyheads have moderately compressed bodies and relatively large heads, armed with eight pairs of robust spines along the top. Their eyes are large, and a horizontal suborbital ridge carries another eight to ten strong spines. The jaws contain many conical teeth, and teeth are also present on the roof of the mouth.

The single dorsal fin is notched behind the spiny section, which has 15 to 17 robust, venom-bearing spines, followed by 8 to 11 soft rays. The anal fin has three spines and four to six soft rays. The caudal fin has a straight edge. Maximum lengths range from 39 cm total length in S. altevelis to 80 cm standard length in S. alascanus.

These fish are demersal, living over soft substrates. They are found in both the eastern and western northern Pacific Ocean, with vagrants reaching as far south as Costa Rica. Unlike rockfishes in the genus Sebastes, thornyheads are oviparous, with females extruding gelatinous egg masses.