''Protanguilla palau'' is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

eel Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 20 families, 164 genera, and about 1000 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...

, the only species in the

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

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

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

, Protanguillidae. Its common name is Palauan primitive cave eel. 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, is an island country in the Micronesia subregion of Oceania in the western Pacific Ocean. The Republic of Palau consists of approximately 340 islands and is the western part of the Caroline Islands ...

. 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. Being a significantly aged cave species, ''Protanguilla palau'' has also been given the name "Palauan primitive cave eel". For this reason it is known as a "

living fossil A living fossil is a Deprecation, deprecated term for an extant taxon that phenotypically 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 or ...

Characteristics

The body is very small and slender, about 18 cm long.'Fossil eel' squirms into the record books

Agence France-Presse Agence France-Presse (; AFP) is a French international news agency headquartered in Paris, France. Founded in 1835 as Havas, it is the world's oldest news agency. With 2,400 employees of 100 nationalities, AFP has an editorial presence in 260 c ...

, 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 mammals h ...

and under 90

vertebrae Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

, 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 th ...

s in its

branchial arch Branchial arches or gill arches are a series of paired bony/ cartilaginous "loops" behind the throat ( pharyngeal cavity) of fish, which support the fish gills. As chordates, all vertebrate embryos develop pharyngeal arches, though the eve ...

es has never previously been found in an eel, but is common in

bony fish Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

. 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 The Mesozoic Era is the era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Periods. It is characterized by the dominance of archosaurian reptiles such as the dinosaurs, and of gymnosperms s ...

. 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 "

References

External links

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