Idiastion is a small genus of marine ray-finned fish belonging to the family Scorpaenidae, the scorpionfishes.

[3] The genus is classified within the tribe Scorpaenini in the subfamily Scorpaeninae of the scorpionfish family Scorpaenidae.

[5] There are currently three recognized species in this genus:[3] Idiastion scorpionfishes have a deep body, deepest behind the head with a hump backed shape.

They have a complete lateral line with tubes on the scales and a small swim bladder.

[3] Idiastion scorpionfishes are found in the western Atlantic Ocean (I. kyphos), the Galápagos Islands (I. hageyi) and around Japan and over the Emperor Seamounts in the northwestern Pacific (I.