[3] The adults are sexually dimorphic and the mature males have elongate rays in their dorsal and caudal fins.

There are three symmetrical brown saddle-like blotches along the back with indistinct darker longitudinal stripes on their second dorsal fin.

[4] They are opportunistic feeders which will prey on whichever suitable prey species are most abundant,[6] it feeds mostly on small invertebrates, such as worms and crustaceans,[7] for example in one study crustaceans were found to make up over 85% of the identifiable diet with the porcelain crab Pisidia longicornis making up 43%.

[5] Common dragonets are an important prey item of Atlantic cod and pouting in the Irish Sea.

[9][4] The eggs, larvae and postlarvae of common dragonets are pelagic[1] while the juveniles prefer the intertidal zone.

[4] This species is of minor importance to local commercial fisheries and can be found displayed in public aquariums.