Lamphreys

Petromyzontiformes - lampreys

 

Vertebrata; Petromyzontiformes
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Lamprey
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Lamprey Mouthparts

The Petromyzontiformes, or lampreys, were once grouped in a taxon called Agnatha (jawless fishes), which also contained the other extant group of jawless fishes, the hagfishes (Hyperotreti). The Agnatha traditionally formed one of the two major sister lineages of vertebrates, the other being the Gnathostomata (jawed vertebrates). Below is a cladogram showing the old view of basal vertebrate phylogeny:


However, it has since been discovered that lampreys are more closely related to jawed vertebrates than are hagfishes, and thus Agnatha is a paraphyletic group. In fact, hagfishes are no longer considered vertebrates in the strict sense, as they do not possess vertebral elements surrounding the dorsal nerve cord - evolutionary precursors to the vertebral column seen in well-known vertebrates. Instead, they are classified as an outgroup to the Vertebrata, collectively forming the monophyletic Craniata. Craniates are defined by the presence of a well-defined head region, with a cranium that encases a brain and paired sensory organs, and includes the last common ancestor of vertebrates and hagfishes plus all its descendents.

Lampreys and jawed vertebrates are therefore considered the two extant clades forming the Vertebrata in its strict sense. The cladogram below illustrates these phylogenetic relationships


Diversity and Lower Taxonomy:

The order Petromyzontiformes comprises a single family, Petromyzontidae, containing 40 extant species of lamprey across ten genera: Petromyzon, Caspiomyzon, Geotria, Mordacia,Eudontomyzon, Tetrapleurodon, Entosphenus, Lethenteron, and Lampetra.



Distribution and Habitat:

Lampreys are distributed amphitropically (in temperate regions north and south of the tropics). Only two genera (Geotria and Mordacia) are present in the Southern Hemisphere, with the remaining eight in the Northern Hemisphere.

Lampreys inhabit either freshwater or marine environments in all temperate regions except those of Africa. All species live in freshwater during their larval stage and also spawn and die in river habitats. Some species are anadromous, migrating to coastal seas when mature and only returning to reproduce. Lamprey larvae have a low tolerance for high water temperature, hence they are not found in tropical regions.

Conservation Status (IUCN):

The IUCN Red List has assessment entries for only 18 of the 40 species of lamprey. Of these, the majority (10 species) are listed as Least Concern (LC). While one species, the Ukrainian migratory lamprey (Eudontomyzon sp. nov. 'migratory'), was confirmed extinct in 2008, another species, the Greek Brook lamprey (Eudontomyzon hellenicus), is Critically Endangered (CR). Two species are considered Near Threatened (NT) and one is Vulnerable (VU), while the remaining species are Data Deficient (DD).


Features:

  • Lack a bony skeleton and jaws (bones may have been secondarily lost, as there is evidence to suggest that their ancestors possessed a bony skeleton).
  • No paired fins (pectoral, pelvic), but do have unpaired fins: dorsal and caudal (tail) fin.
  • Presence of horny teeth, which they use as a "rasping tongue" to suck on to prey, and pierce the flesh to draw blood.
  • Rows of paired gill openings; water flows in and out of the gills in a tidal flow - while most fish breathe by drawing water into the mouth, past the gills, and out through the gill slits in a one-way flow of water, lampreys cannot use their mouths for ventilation as they are attached to prey!

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