Lamprey

Lampreys (sometimes inaccurately called lamprey eels) are an ancient extant lineage of jawless fish of the order Petromyzontiformes, placed in the superclass Cyclostomata. The adult lamprey may be characterized by a toothed, funnel-like sucking mouth. The common name 'lamprey' is probably derived from Latin lampetra, which may mean 'stone licker' (lambere 'to lick' + petra 'stone'), though the etymology is uncertain. The plural form lamprey is sometimes seen. There are about 38 known extant species of lampreys and five known extinct species. Parasitic carnivorous species are the most well-known, and feed by boring into the flesh of other fish to suck their blood; but only 18 species of lampreys engage in this micropredatory lifestyle. Of the 18 carnivorous species, nine migrate from saltwater to freshwater to breed (some of them also have freshwater populations), and nine live exclusively in freshwater. All non-carnivorous forms are freshwater species. Adults of the non-carnivorous species do not feed; they live off reserves acquired as ammocoetes (larvae), which they obtain through filter feeding. Lampreys live mostly in coastal and fresh waters and are found in most temperate regions except those in Africa. 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. Other species are found in land-locked lakes. 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. In Britain, at the time of the Conquest, lampreys were found as far upstream in the River Thames as Petersham. The reduction of pollution in the Thames and River Wear has led to recent sightings in London and Chester-le-Street. Distribution of lampreys may also be adversely affected by dams and other construction projects due to disruption of migration routes and obstruction of 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. Active control programs to control lampreys are undergoing modifications due to concerns of drinking water quality in some areas. Adults superficially resemble eels in that they have scaleless, elongated bodies, and can range from 13 to 100 cm (5 to 40 inches) in length. 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. The pharynx is subdivided; the ventral part forming a respiratory tube that is isolated from the mouth by a valve called the velum. This is an adaptation to how the adults feed, by preventing the prey's body fluids from escaping through the gills or interfering with gas exchange, which takes place by pumping water in and out of the gill pouches instead of taking it in through the mouth. Near the gills are the eyes, which are poorly developed and buried under skin in the larvae. The eyes consummate their development during metamorphosis, and are covered by a thin and transparent layer of skin that becomes opaque in preservatives.