Tuesday, June 3, 2008

Lamprey

Lamprey in Indonesia called "Belut Lamprey", and hagfishes are the two surviving groups of jawless vertebrates. The earliest known lampreys, genus Mayomyzon, are from the Pennsylvanian Period, about 300 million years ago, and are thought to be closely related to an extinct group of jawless fishes, the ostracoderms, which flourished earlier. Lamprey is eel-like in shape and lack scales and paired fins (pectorials and pelvics), but they do have a tail and one or two dorsal (top) fins. In place of jaws, lampreys have an oral sucking disk bearing teeth and a rasplike tongue. The internal body support consists of notochord ("backbone") and a cartilaginous skeleton. Lamprey have seven separate gill openings on each side and a single nostril on the upper part of the head.

Some lampreys live only in fresh water. Other species are anodromous, living in marine waters but breeding in fresh water. Lamprey are found in cold to cool coastal and inland waters of both the Northern and Southern hemispheres, with the exception of all of Africa but the northwestern tip.

Although individuals within a single lamprey species may be either parasitic or non-parasitic, it is more usual for a species to be exclusively one or the other. When lamprey hatch they develop into small, blind, toothless, almost wormlike larvae called ammocetes, which burrow in the stream bottom. Ammocetes are filter feeders, straining tiny organisms from the water for food. After several years the ammocetes metamorphose, or change, into the adult form. If the species or individual is non-parasitic, the digestive system degenerates and the adult neither feeds nor grows, merely surviving long enough to reproduce. If parasitic, the adult will adhere to the bodies of the other fish with its sucking disk and then rasp their flesh to feed their blood and tissue.

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