Ammocoetes
| Lamprey Temporal range: Late Devonian–Holocene |
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| A European river lamprey (Lampetra fluviatilis) | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Hyperoartia |
| Order: |
Petromyzontiformes Berg, 1940 |
| Families | |
† = extinct |
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† = extinct
Lampreys (sometimes also called, inaccurately, lamprey eels) are any 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" ( "to lick" + "stone"), though the etymology is uncertain.
Currently there are about 38 known extant species of lampreys. Parasitic species are the best known, and feed by boring into the flesh of other fish to suck their blood; but only 18 species of lampreys are parasitic. Adults of the non-parasitic species do not feed; they live off reserves acquired as ammocoetes (larvae), which they obtain through filter feeding.
The lampreys are a very ancient lineage of vertebrates, though their exact relationship to hagfishes and jawed vertebrates is still a matter of dispute.
Basic external anatomy of a lamprey
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 complete their development during metamorphosis, and in adults are covered by a thin and transparent layer of skin that becomes opaque in preservatives.
The unique morphological characteristics of lampreys, such as their cartilaginous skeleton, suggest they are the sister taxon (see cladistics) of all living jawed vertebrates (gnathostomes), and are usually considered the most basal group of the Vertebrata. Instead of true vertebrae, they have a series of cartilaginous structures called arcualia arranged above the notochord. Hagfish, which resemble lampreys, have traditionally been considered the sister taxon of the true vertebrates (lampreys and gnathostomes) but DNA evidence suggests that they are in fact the sister taxon of lampreys.
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Wikipedia