The longspined bullhead is a small fish with a thick, tapering body and a large head and resembles the shorthorn sculpin (Myoxocephalus scorpius). It has two spines on each side on the gill cover, the front one extending further than the rear one. The skin is not clad in scales. There is a row of bony tubercles running along the flank on the lateral line and there are backward sloping bony tubercles on the crown of the head. It has a variety of colours ranging from shades of brown or olive green, with cream blotches and four dark, vertical bands. The belly is pale bluish-green but becomes suffused with red in males in the breeding season.
Bullhead are predators that will eat prawns, molluscs and small fish such as gobies and blennies. Despite their small size they are aggressive and will attack fish bigger than themselves. They lie in wait for prey, camouflaged against rocks and weed before striking out at anything that passes. Like all fish in the Cottidae family, the bullhead does not have a swim bladder, meaning that it sinks as soon as it stops swimming. Breeding takes place in early spring and fertilisation is internal, however the reproduction of this species has been little studied.
Other English names for this species include sea scorpion, bullhead, rockfish, rock sculpin, scorpion fish, clobberhead.