''Protanguilla palau'' is a

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 ...

eel Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...

, the only species in the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

''Protanguilla'' (first eel), which is in turn the only genus in its

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

, Protanguillidae. Individuals were found swimming in March 2010 in a deep underwater cave in a

fringing reef A fringing reef is one of the three main types of coral reef. It is distinguished from the other main types, barrier reefs and atolls, in that it has either an entirely shallow backreef zone (lagoon) or none at all. If a fringing reef grows direc ...

off the coast of

Palau Palau,, officially the Republic of Palau and historically ''Belau'', ''Palaos'' or ''Pelew'', is an island country and microstate in the western Pacific. The nation has approximately 340 islands and connects the western chain of the ...

. Protanguillidae is a sister group to all other eels.Springer, V. G. (2015). The Gill-Arch Musculature of Protanguilla, the Morphologically Most Primitive Eel (Teleostei: Anguilliformes), Compared with That of Other Putatively Primitive Extant Eels and Other Elopomorphs, 103(2), 595–620. doi: 10.1643/CI-14-152 They are monophyletic, yet also strongly synapomorphic with all other eel species. Molecular analysis shows that all other eels are also monophyletic, showing that they may have broken off directly from the Protanguillidae. for this reason it's known as a "Living Fossil."

Characteristics

The body is very small and slender, about 18 cm long.'Fossil eel' squirms into the record books
Agence France-Presse, 16 August 2011. The eel has a second

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

and under 90

vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

, features previously found only in fossilised eels. Its full set of

gill raker Gill rakers in fish are bony or cartilaginous processes that project from the branchial arch (gill arch) and are involved with suspension feeding tiny prey. They are not to be confused with the gill filaments that compose the fleshy part of the ...

s in its

branchial arch Branchial arches, or gill arches, are a series of bony "loops" present in fish, which support the gills. As gills are the primitive condition of vertebrates, all vertebrate embryos develop pharyngeal arches, though the eventual fate of these arc ...

es has never previously been found in an eel, but is common in bony fish. It is very different from all other living eels, and scientists estimate it must have diverged from the others around 200 million years ago, during the Mesozoic era. It thus has not only its own species, but also its own genus and

, as well, and has been referred to by scientists as a "

living fossil A living fossil is an extant taxon that cosmetically resembles related species known only from the fossil record. To be considered a living fossil, the fossil species must be old relative to the time of origin of the extant clade. Living foss ...

References

External links

Youtube video
Eels Fish of the Pacific Ocean Monotypic fish genera Fish described in 2012 {{Anguilliformes-stub