River Lamprey Lampetra fluviatilis
The river lamprey is a primitive, jawless fish, with a round, sucker-mouth which it uses to attach to other fish to feed from them. They have long elongated eel-like bodies and can be recognised by their gills which open directly to each side of the head and form a line of seven gill holes behind the eye. Adults live in the sea and return to freshwater to spawn. Image: Hans Hillewaert (iNaturalist).