The body is very elongated and can exceed 80 cm in length. There are seven pairs of gill openings in the head area. The mouth is formed by a disc covered with strong teeth. Body color is gray-greenish or brown, with irregular dark spots.

The sea lamprey is an anadromous species that lives in the sea and reproduce in rivers. It is distributed throughout the Atlantic and the Mediterranean. In Catalonia it is only known that it enters the river Ebro, although it has not been detected for many years.

Adults enter rivers in the spring to reproduce, and die after spawning. The larvae are filter-feeding and live buried in the mud. After a few years, they migrate to the sea, where they feed on the blood of other fish that suck through their buccal disc.