''Rubicundus'' is a

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 ...

hagfish Hagfish, of the Class (biology), class Myxini (also known as Hyperotreti) and Order (biology), order Myxiniformes , are eel-shaped Agnatha, jawless fish (occasionally called slime eels). Hagfish are the only known living Animal, animals that h ...

es, the only extant member of the

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...

Rubicundinae. All species in it were formerly classified in ''

Eptatretus ''Eptatretus'' is a large genus of hagfish. Species There are currently 50 recognized species in this genus: * '' Eptatretus aceroi'' Polanco Fernández & Fernholm, 2014 (Acero's hagfish)Polanco Fernandez, A. & Fernholm, B. (2014): A New Speci ...

''. ''R. eos'', ''R. lakeside'', and ''R. rubicundus'' are known from single specimens caught in the

Tasman Sea The Tasman Sea is a marginal sea of the South Pacific Ocean, situated between Australia and New Zealand. It measures about across and about from north to south. The sea was named after the Dutch explorer Abel Janszoon Tasman, who in 1642 wa ...

, Galápagos, and

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main geography of Taiwan, island of Taiwan, also known as ''Formosa'', lies between the East China Sea, East and South China Seas in the northwestern Pacific Ocea ...

, respectively. They are named after the distinctive red coloration that all species share. They represent the sister lineage to all other extant lineages of hagfishes, and may represent the

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

fossil hagfish ''

Tethymyxine ''Tethymyxine'' is an extinct genus of hagfish known from the Late Cretaceous (Cenomanian) of Lebanon. It contains a single species, ''Tethymyxine tapirostrum'', known from a single fossil specimen. It is the oldest crown group hagfish known fro ...

'', from which they potentially diverged during the

Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

. Both ''Rubicundus'' and ''Tethymyxine'' share an elongate snout, indented barbels, and numerous slime glands. Phylogenetic studies indicate that the Rubicundinae lineage may have diverged from other extant hagfishes during the

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

, making them an extremely old lineage.

Species

Four recognized species are placed in this genus: * '' Rubicundus eos'' ( Fernholm, 1991) (pink hagfish) * '' Rubicundus lakeside'' ( Mincarone & J. E. McCosker, 2004) (Lakeside hagfish) * '' Rubicundus lopheliae'' ( Fernholm & Quattrini, 2008) (Lophelia hagfish) * '' Rubicundus rubicundus'' ( C. H. Kuo, S. C. Lee & H. K. Mok, 2010)

References

Myxinidae Jawless fish genera {{jawless-fish-stub