Blennies (from the Greek ἡ βλέννα and τό βλέννος, mucus, slime) are a diverse clade of ray-finned fish in the suborder Blennioidei of the percomorph order Blenniiformes. They inhabit marine, brackish, and occasionally freshwater habitats, and generally share similar morphology and behaviour. About 151 genera and nearly 900 species have been described within the order.