Lamprey
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[Photo] Mouth of an European river lamprey (Lampetra fluviatilis). Boca de lamprea en la Sala Maremagnum del Aquarium Finisterrae (Casa de los Peces), en La Coru??a, Galicia, Espa??a. Date 13:44, 25 April 2007. Author Drow_male http://commons.wikimedia.org/wiki/User:Drow_male

A lamprey (sometimes also called lamprey eel) is a jawless fish with a toothed, funnel-like sucking mouth. While lampreys are well known for those species which bore into the flesh of other fish to suck their blood, these species make up the minority. In zoology, lampreys are often not considered to be true fish because of their vastly different morphology and physiology.

Physical description
Lampreys live mostly in coastal and fresh waters, although at least one species, Geotria australis, probably travels significant distances in the open ocean, as is evidenced by the lack of reproductive isolation between Australian and New Zealand populations, and the capture of a specimen in the Southern Ocean between Australia and Antarctica. They are found in most temperate regions except Africa. Their larvae have a low tolerance for high water temperatures, which is probably why they are not found in the tropics. Outwardly resembling eels, in that they have no scales, an adult lamprey can range anywhere from 13 to 100 centimetres (5 to 40 inches) long. Lampreys have no paired fins, large eyes, one nostril on the top of the head, and seven gills on each side. The unique morphological characteristics of lampreys, such as their cartilaginous skeleton, means that they are the sister taxon (see cladistics) of all living jawed vertebrates (gnathostomes) and are not classified within the Vertebrata itself. This is disputed by some, who place lampreys within Vertebrata. (The hagfish, which superficially resembles the lamprey, is the sister taxon of the lampreys and gnathostomes (a clade termed the Craniata).

Lampreys begin life as burrowing freshwater larvae (ammocoetes). At this stage, they are toothless, have rudimentary eyes, and feed on microorganisms. This larval stage can last five to seven years and hence was originally thought to be an independent organism. After these five to seven years, they transform into adults in a metamorphosis which is at least as radical as that seen in amphibians, and which involves a radical rearrangement of internal organs, development of eyes and transformation from a mud-dwelling filter feeder into an efficient swimming predator, which typically moves into the sea to begin a predatory/parasitic life, attaching their mouth to a fish, secreting an anticoagulant to the host, and feeding on the blood and tissues of the host. In most species this phase lasts about 18 months.

Not all lampreys can be found in the sea. Some lampreys are landlocked and remain in fresh water, and some of these stop feeding altogether as soon as they have left the larval stage. The landlocked species are usually rather small.

To reproduce, lampreys return to fresh water (if they left it), build a nest, then spawn, that is, lay their eggs or excrete their semen, and then invariably die. In Geotria australis, the time between ceasing to feed at sea and spawning can be up to 18 months.

Recent studies reported in Nature suggest that lampreys have evolved a unique type of immune system with parts that are unrelated to the antibodies found in mammals. They also have a very high tolerance to iron overload, and have evolved biochemical defenses to detoxify this metal.

Fossil lampreys
Lamprey fossils are rare; cartilage does not fossilize as readily as bone. Until 2006, the oldest known fossil lampreys were from Early Carboniferous limestones, laid down in marine sediments in North America: Mayomyzon pieckoensis and Hardistiella montanensis. In the 22 June 2006 issue of Nature, Mee-mann Chang and colleagues reported on a fossil lamprey from the same Early Cretaceous lagerst??tten that have yielded feathered dinosaurs, in the Yixian Formation of Inner Mongolia. The new species, morphologically similar to Carboniferous and modern forms, was given the name Mesomyzon mengae ("Middle lamprey"). The exceedingly well-preserved fossil showed a well-developed sucking oral disk, a relatively long branchial apparatus showing branchial basket, seven gill pouches, gill arches and even the impressions of gill filaments, as well as about 80 myomeres of its musculature.

A few months later, in the 27 October issue of Nature, an even older fossil lamprey, dated 360 million years ago, was reported from Witteberg Group rocks near Grahamstown, in the Eastern Cape of South Africa. This species, dubbed Priscomyzon riniensis still strongly resembled modern lampreys despite its Devonian age.

Taxonomy
The taxonomy presented here is that given by Fisher, 1994. This work classifies lampreys as the sole living members of the class Cephalaspidomorphi. The lampreys entail the single order Petromyzontiformes and family Petromyzontidae.

Within this family, there are 40 recorded species in nine genera and three subfamilies:

Subfamily Geotriinae
Genus Geotria
Pouched lamprey, Geotria australis (Gray,1851)
Subfamily Mordaciinae
Genus Mordacia
Mordacia lapicida (Gray, 1851)
Mordacia mordax (Richardson, 1846)
Mordacia praecox (Potter, 1968)
Subfamily Petromyzontinae
Genus Caspiomyzon
Caspiomyzon wagneri (Kessler, 1870)
Genus Eudontomyzon
Eudontomyzon danfordi (Regan, 1911)
Eudontomyzon hellenicus (Vladykov, Renaud, Kott and Economidis, 1982)
Eudontomyzon mariae (Berg, 1931)
Eudontomyzon morii (Berg, 1931)
Eudontomyzon stankokaramani (Karaman, 1974)
Eudontomyzon vladykovi (Oliva and Zanandrea, 1959)
Genus Ichthyomyzon
Ichthyomyzon bdellium (Jordan, 1885) - Ohio lamprey
Ichthyomyzon castaneus Girard, 1858 - chestnut lamprey
Ichthyomyzon fossor (Reighard and Cummins, 1916) - northern brook lamprey
Ichthyomyzon gagei (Hubbs and Trautman, 1937) - southern brook lamprey
Ichthyomyzon greeleyi (Hubbs and Trautman, 1937) - mountain brook lamprey
Ichthyomyzon unicuspis (Hubbs and Trautman, 1937) - silver lamprey
Genus Lampetra
Lampetra aepyptera (Abbott, 1860) - least brook lamprey
Lampetra alaskensis (Vladykov and Kott, 1978)
Lampetra appendix (DeKay, 1842) - American brook lamprey
Lampetra ayresii (G??nther, 1870)
Lampetra fluviatilis (Linnaeus, 1758)
Lampetra hubbsi (Vladykov and Kott, 1976) - Kern brook lamprey
Lampetra lamottei (Lesueur, 1827)
Lampetra lanceolata (Kux and Steiner, 1972)
Lampetra lethophaga (Hubbs, 1971) - Pit-Klamath brook lamprey
Lampetra macrostoma (Beamish, 1982) - Vancouver lamprey
Lampetra minima (Bond and Kan, 1973) - Miller Lake lamprey
Lampetra planeri (Bloch, 1784)
Lampetra richardsoni (Vladykov and Follett, 1965) - western brook lamprey
Lampetra similis (Vladykov and Kott, 1979) - Klamath lamprey
Lampetra tridentata (Richardson, 1836) - Pacific lamprey
Genus Lethenteron
Lethenteron camtschaticum (Tilesius, 1811)
Lethenteron japonicum (Martens, 1868)
Lethenteron kessleri (Anikin, 1905)
Lethenteron matsubarai (Vladykov and Kott, 1978)
Lethenteron reissneri (Dybowski, 1869)
Lethenteron zanandreai (Vladykov, 1955)
Genus Petromyzon
Petromyzon marinus (Linnaeus, 1758) - sea lamprey
Genus Tetrapleurodon
Tetrapleurodon geminis (Alvarez, 1964)
Tetrapleurodon spadiceus (Bean, 1887)

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