Information from Wikipedia.
Lampreys (sometimes also called lamprey eels) are an order of jawless fish, the adult of which is characterized by a toothed, funnel-like sucking mouth. Currently there are about 38 known species of lampreys. Although they are well known for boring into the flesh of other fish to suck their blood, in fact only a minority do so; only 18 species of lampreys are actually parasitic.
Adults physically resemble eels, in that they have no scales, and can range from 13 to 100 cm (5.0 to 40 inches) long. Lacking paired fins, adult lampreys have large eyes, one nostril on the top of the head, and seven gill pores on each side of the head. Parasitic lampreys feed on prey as adults by attaching their mouthparts to the target animal's body, then using their teeth to cut through surface tissues until they reach blood and body fluid.
Lampreys live mostly in coastal and fresh waters, although some species (e.g. Geotria australis, Petromyzon marinus, and Entosphenus tridentatus) travel significant distances in the open ocean, as evidenced by their lack of reproductive isolation between populations. Some species are found in land-locked lakes. They are found in most temperate regions except those in Africa. Their larvae (ammocoetes) have a low tolerance for high water temperatures, which may explain why they are not distributed in the tropics.
Lamprey distribution may be adversely affected by overfishing and pollution.
Distribution may also be adversely affected by dams and other construction projects disrupting migration routes, obstructing access to spawning grounds. Conversely, the construction of artificial channels has exposed new habitats for colonisation notably in North America where sea lampreys have become a significant introduced pest in the Great Lakes.
Family Geotriidae – pouched lamprey Genus Geotria
Family Mordaciidae – southern topeyed lampreys Genus Mordacia
Family Petromyzontidae – northern lampreys