Lamprey, the popular name for any vertebrate of the Cyclostome family Petromyzontidae. The body is eel-shaped and naked, the skeleton cartilaginous, and there is a single nostril on the upper side of the head, and behind the head on each side are seven branchial pouches. The larvae undergo a metamorphosis. Lampreys are widely distributed in the rivers and round the coasts of the north and south temperate zones. Little is known of their habits, but some ascend rivers to spawn, and in fresh water the young undergo their metamorphosis, which takes from three to four years to complete. They feed on dead aquatic animals, thus acting as scavengers, and on crustaceans, and attach themselves to fish by means of their suctorial mouth, eating into the flesh of their victims, who are unable to shake off their enemies. Dr. Gunther records the fact that salmon have been taken in the Rhine with the Sea Lamprey attached to them. The type-genus Petromyzon, from the northern hemisphere, has two dorsal fins, the hinder one continuous with the caudal. There are three British species - the Sea Lamprey (P. marinus), about 3 feet long, from the coasts of Europe and North America; the River Lamprey (P.fluviatilis), about 2 feet long; and Lampern, Pride, or Sandpiper (P. branchialis), about half that size. The larva of the last-named form was long thought to be quite distinct, and was formerly placed in a separate genus. [Ammocete.] Its toothless mouth is fringed with barbules, the small eyes are hidden in a groove, and there is a single continuous vertical fin. Lampreys have long been esteemed for food, and G. A. Sala states that a large number of the "eel-pies" sold in London are made from Thames Lamperns.