''Phreatobius'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of very small

catfish Catfish (or catfishes; order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the three largest species alive, ...

es ( order Siluriformes) from tropical South America.

Taxonomy

For quite some time ''Phreatobius cisternarum'' was the only

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

in the genus. However, two new species were described relatively recently in 2007, ''Phreatobius dracunculus'' and ''Phreatobius sanguijuela''. ''Phreatobius'' has been classified with a number of different families: Clariidae, Plotosidae,

Trichomycteridae Trichomycteridae is a family of catfishes commonly known as pencil catfishes or parasitic catfishes. This family includes the candiru fish (''Vandellia cirrhosa''), feared by some people for its alleged habit of entering into the urethra of hum ...

Cetopsidae The Cetopsidae are a small family of catfishes ( order Siluriformes), commonly called the whale catfishes. Taxonomy This family contains five genera divided into two subfamilies, Cetopsinae and Helogeneinae. Helogeneinae was previously a family ...

, and

Pimelodidae The Pimelodidae, commonly known as the long-whiskered catfishes, are a family of catfishes ( order Siluriformes). Taxonomy The family Pimelodidae has undergone much revision. Currently, it contains about 30 genera and about 90 recognized and kno ...

. Most recently, it has been classified in

Heptapteridae The Heptapteridae, or three-barbeled catfishes, are a family of catfish that originate from the Americas. Most species are restricted to South America, but ''Imparfinis lineatus'', '' Nemuroglanis panamensis'' and ''Pimelodella chagresi'' are na ...

. Its

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

position remains uncertain. The

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

placement of the genus has remained problematic and thus it is not classified in any of the existing families, though

Fishbase FishBase is a global species database of fish species (specifically finfish). It is the largest and most extensively accessed online database on adult finfish on the web.

treats it as a member of Heptapteridae. An

undescribed species In taxonomy, an undescribed taxon is a taxon (for example, a species) that has been discovered, but not yet formally described and named. The various Nomenclature Codes specify the requirements for a new taxon to be validly described and named. U ...

of ''Phreatobius'' lives in waterlogged

leaf litter Plant litter (also leaf litter, tree litter, soil litter, litterfall or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that have fallen to the ground. This detritus or dead organic material and its constituent ...

near (not in) streams. ''Phreatobius walkeri'', a '' nomen nudum'', is provided by the

Guinness Book of World Records ''Guinness World Records'', known from its inception in 1955 until 1999 as ''The Guinness Book of Records'' and in previous United States editions as ''The Guinness Book of World Records'', is a reference book published annually, listing world ...

, to describe this fish that stays on land for extended periods of time. Two additional quite distinctive species of ''Phreatobius'', as yet undescribed, are known from the Río Negro basin of Brazil.

Species

There are currently three recognized species in this genus: * ''

Phreatobius cisternarum ''Phreatobius cisternarum'' is a species of catfish in the genus ''Phreatobius''. This Brazilian fish is one of the few fish species that Cavefish, live underground in phreatic habitats. It has proved problematic in its classification.Muriel-Cunh ...

'' Goeldi, 1905 * '' Phreatobius dracunculus'' Shibatta, Muriel-Cunha &

de Pinna De Pinna was a high-end clothier for men and women founded in New York City in 1885, by Alfred De Pinna (1831 - 1915), a Sephardic Jew born in England. They also sold menswear-inspired clothing for women that was finely tailored. The flagship sto ...

, 2007 * '' Phreatobius sanguijuela'' L. A. Fernández, Saucedo, Carvajal-Vallejos & S. A. Schaefer, 2007

Distribution and habitat

The three scientifically described ''Phreatobius'' species all live underground and are known only from artificial wells penetrating near-surface aquifers of the

Amazon basin The Amazon basin is the part of South America drained by the Amazon River and its tributaries. The Amazon drainage basin covers an area of about , or about 35.5 percent of the South American continent. It is located in the countries of Bolivi ...

. The genus has one of the widest distribution of any hypogean fish genus, with ''P. sanguijuela'' from the upper Amazon, some 2000 km from reported locations of ''P. cisternarum'' near the Amazon River mouth, and ''P. dracunculus'' also approximately 1900 km from the Rio Branco drainage area.

Description

This genus can be recognized by the combination of characteristics, such as their dorsal and anal fins being continuous with a rounded

caudal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

, unbranched

anal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

rays, a projecting lower jaw, bright red coloration, a lack of the

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...

spine locking mechanism, the first

pectoral fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...

ray being soft instead of spinous. Most of these traits are rare or unusual among vast groups of catfish. All three species look extremely similar. However, in ''P. cisternarum'' the eyes are tiny, while ''P. dracunculus'' and ''P. sanguijuela'' lack eyes altogether. The two eyeless species can be differentiated by fin-ray and vertebrae counts. It is also described that ''P. dracunculus'' is lighter in color, while ''P. cisternarum'' and ''P. sanguijuela'' are described as bright red.

References

{{Taxonbar, from=Q2103561 Catfish of South America Catfish genera Taxa named by Émil Goeldi Heptapteridae