Pholis gunnellus has an elongate, laterally compressed body up to 25 cm long. This fish has thick fleshy lips and small, conical teeth. A black stripe is present through the eye.The dorsal fin is long, consisting of 75-82 spines, begins just behind the head and reaches to the base of the caudal fin. A series of around 12 distinctive black spots, outlined in white are present along the base of the dorsal fin. The pelvic fin is reduced to a minute spine. The anal fin is long with 39-45 soft fin rays. The caudal fin is rounded. The butterfish is yellowish to reddish brown with irregular darker vertical bars or a mottled pattern on the body.Pholis gunnellus is related to Chirolophis ascani (Yarell's blenny) and together these belong to a group called the Arctic blennies (Dipper, 2001). The butterfish is unusual in that both parents may take turns to guard the eggs. The name 'butterfish' derives from the slimy skin of this fish.