Beardfish

The beardfishes consist of a single extant genus, Polymixia, of deep-sea marine ray-finned fish named for their pair of long hyoid barbels. They are classified in their own order Polymixiiformes. But as Nelson says, "few groups have been shifted back and forth as frequently as this one, and they were recently added to Paracanthoptergii". For instance, they have previously been classified as belonging to the Beryciformes, and are presently considered either paracanthopterygians or the sister group to acanthopterygians. They are of little economic importance.
They are found in tropical and subtropical waters of the Atlantic, Indian and western Pacific Ocean. They are bottom-dwelling fish, found down to about depth. Most are relatively small fish, although one species, Polymixia berndti, is over in length.
The earliest body fossils are from the Late Cenomanian of Lebanon, of the genus Pycnosteroides. However, tentative earlier records are known from distinctive fossil otoliths from the Early Cretaceous of Texas, USA. Many different fossil families and genera are known from the Late Cretaceous and early Cenozoic, in contrast to the relatively few surviving species in a single genus. Extant beardfish can thus be considered "living fossils".

Classification

Order Polymixiiformes Rosen & Patterson, 1969
* Genus ?†Allocyclostoma Schwarzhans, Stringer & Welton, 2022
**†A. alienus Schwarzhans, Stringer & Welton, 2022
* Genus †Cumbaaichthys Murray 2016
** †Cumbaaichthys oxyrhynchus Murray 2016
*Genus †Severnichthys Stringer & Schwarzhans, 2021
**†S. beauryi
**†S. bourdoni Stringer & Schwarzhans, 2021
*Genus ?†Texoma Schwarzhans, Stringer & Welton, 2022
**†T. cyclogaster Schwarzhans, Stringer & Welton, 2022
* Family †Boreiohydriidae Murray & Cumbaa 2013
** Genus †Boreiohydrias Murray & Cumbaa 2013
*** †Boreiohydrias dayi Murray & Cumbaa 2013
* Family †Dalmatichthyidae Radovčić 1975
** Genus †Dalmatichthys Radovčić 1975
*** †Dalmatichthys malezi Radovčić 1975
* Family †Digoriidae Bannikov 1985
** Genus †Digoria Daniltshenko, 1980
*** †Digoria ambigua Daniltshenko, 1980
* Family †Dinopterygidae Jordan, 1923
** Genus †Dinopteryx Woodward, 1901
*** †Dinopteryx spinosus
* Family Polymixiidae Gill 1862
** Genus †Apricenaichthys Taverne 2011
*** †Apricenaichthys italicus
** Genus †Berycopsia Radovčić 1975
*** †Berycopsia inopinnata Radovčić 1975
** Genus †Berycopsis Dixon 1850
*** †B. elegans Dixon 1850
*** †B. germana
*** †B. pulcher Bannikov & Bacchia 2004
**Genus †Cowetaichthys Schwarzhans, Huddleston & Takeuchi, 2018
***†C. alabamae Schwarzhans, Huddleston & Takeuchi, 2018
***†C. beauryi
***†C. carnevalei Schwarzhans & Stringer, 2020
***†C. groenlandicus
***†C. harderi
***†C. lamberi Schwarzhans, Huddleston & Takeuchi, 2018
** Genus †Homonotichthys Whitley 1933
*** †H. dorsalis
*** †H. elegans
*** †H. rotundus
**Genus †Namicauda Schwarzhans, Ohe & Ando, 2017
***†Namicauda pulvinata Schwarzhans, Ohe & Ando, 2017
** Genus †Omosoma Costa 1857
*** †O. garretti Bardack 1976
*** †O. pulchellum Davis 1887
*** †O. sahelalmae Costa 1857
*** †O. tselfatense Gaudant 1978
** Genus †Omosomopsis Gaudant 1978
*** †Omosomopsis sima Gaudant 1978
** Genus †Parapolymixia David 1946
*** †Parapolymixia californica David 1946
** Genus †Pycnosterinx Heckel 1849
*** †P. discoides Heckel 1849
*** †P. dorsalis Pictet 1850
*** †P. heckelii Pictet 1850
*** †P. latus Davis 1887
*** †P. russeggeri Heckel 1849
** Genus Polymixia Lowe 1836
*** P. berndti Gilbert 1905
*** P. busakhini Kotlyar 1993
*** P. carmenae Caixeta, Oliveira & de Melo, 2024
*** P. fusca Kotthaus 1970
*** †?P. harderi
*** P. hollisterae Grande & Wilson, 2021
*** P. japonica Günther 1877
*** P. longispina Deng, Xiong & Zhan 1983
*** P. lowei Günther 1859
*** P. nobilis Lowe 1838
*** †P. polita Schwarzhans 2012
*** P. salagomeziensis Kotlyar 1991
*** P. sazonovi Kotlyar 1992
*** P. yuri Kotlyar 1982
**Genus †Polyspinatus Schrøder, Rasmussen, Møller & Carnevale, 2022
***†Polyspinatus fluere Schrøder, Rasmussen, Møller & Carnevale, 2022
*Family †Pycnosteroididae Patterson, 1964
**Genus †Magrebichthys Murray & Wilson 2014
*** †Magrebichthys nelsoni Murray & Wilson 2014
**Genus †Pycnosteroides Woodward, 1942
***†''Pycnosteroides levispinosus''