Illustration of a sea lamprey (Petromyzon marinus, left), the open mouth of a lamprey (centre) and a European river lamprey (Lampetra fluviatilis). Lampreys are jawless fish that are parasites of many other types of fish. A lamprey will attach itself by its mouth to the skin of its prey and rasp through it with its rough tongue. It then sucks blood and flesh from its victim. Illustration published in 1830.