Alepisauroidei

Sabertooth Evermannella balbo, copyright Fran Martín de la Sierra.

Belongs within: Aulopiformes.
Contains: Paralepididae.

Hunters in the deep sea
21 June 2011
Longnose lancetfish Alepisaurus ferox, photographed by Paulo De Oliveira.

For today’s post, I’m going to tackle the Alepisauroidei. The exact scope of this clade of fishes has changed a bit between authors; here, I’m focusing on the restricted sense used by Sato & Nakabo (2002). In contrast, Davis & Fielitz (2010) used ‘Alepisauroidei’ in a broader sense that combined the Alepisauroidei, Chlorophthalmoidei and Giganturoidei of the former authors; if I have to refer to this larger clade, it’ll be as ‘Alepisauroidei sensu lato‘.

Tedious definitionising aside, the Alepisauroidei sensu stricto include the living families Scopelarchidae, Evermannellidae, Alepisauridae and Paralepididae. All members of these families are predators in the mesopelagic zone of the ocean, below the level of the light. Members of the Alepisauridae (lancetfishes) and Paralepididae (barracudinas) are elongate, reaching lengths of over a metre in the case of the lancetfishes. Many mesopelagic fish migrate closer to the surface at night, and Bond (1996) refers to lancetfishes being caught by anglers standing on the shore during spring in the Pacific Northwest of North America. The predatory nature of the alepisauroids, as well as something of their general appearance, can be inferred from the common names given to many of them: as well as the barracudinas already mentioned, there are the sabretooth fishes of the Evermannellidae, and the daggertooth Anotopterus pharao.

An array of alepisauroids, from here. Species shown are: (Paralepididae) (1) Stemonosudis rothschildi, (2) Lestidium atlanticum, (3) Lestrolepis intermedia, (Evermannellidae) (4) Coccorella atlantica, (5) Evermannella indica, (Scopelarchidae) (6) Scopelarchus analis.

Alepisauroids show many of the adaptations common among deep-water fishes, such as the presence of bioluminescent organs (absent in Alepisauridae) and thin-walled, distensible stomachs allowing the immediate engulfment of large prey items. In the evermannellid genus Coccorella, the caecum of the intestine has become expanded to the extent that part of it actually extends into the animal’s head and can be seen in the base of the oral cavity (Wassersug & Johnson 1976). The members of the family Scopelarchidae are known as pearleyes due to their enlarged, dorsally-directed tubular eyes (also present in the Evermannellidae) that presumably increase their ability to detect the limited light filtering down from above (and, more importantly, from the bioluminescent organs of other mesopelagic animals). Another notable adaptation to the mesopelagic environment present in all alepisauroids is that they are simultaneous hermaphrodites: each individual has fully functional male and female reproductive organs. In an environment where the usual scarcity of food items means that species exist at very low population densities, simultaneous hermaphroditism means that any other individual of your species is a potential mate. Simultaneous hermaphroditism is also found in other members of the Alepisauroidei sensu lato, making it the largest clade of vertebrates utilising this reproductive strategy (Davis & Fielitz 2010).

Specimen of daggertooth Anotopterus vorax, photographed by Peter Marriott.

A comprehensive investigation of the molecular phylogeny of alepisauroids was published by Davis & Fielitz (2010). Evermannellids and scopelarchids were resolved as successive sister groups to the other alepisauroids sensu stricto, suggesting that their tubular eyes may have arisen independently (as corroborated by their absence in the evermannellid genus Odontostomops; alternatively, tubular eyes could have been lost in other alepisauroids). The Alepisauridae were nested within an apparently paraphyletic Paralepididae. The clade as a whole was suggested by molecular dating to have diverged some time in the Early Cretaceous, a result in concordance with the known fossil record.

Systematics of Alepisauroidei
Alepisauroidei
| i. s.: Polymerichthys [Polymerichthyidae]P93
| `--P. nagurai Uyeno 1967P93
|--+--ParalepididaeSN02
| `--AlepisauridaeB-RB13
| |--Anotopterus [Anotopteridae, Anotopteroidei]ND13
| | `--A. pharao Zugmayer 1911PN99b
| `--+--Omosudis [Omosudidae]SN02
| | `--O. lowei Günther 1887PN99d
| `--Alepisaurus Lowe 1833T02, G01 [incl. Plagyodus Steller in Pallas 1811 (nom. inv.)G01]
| |--A. brevirostris Gibbs 1960PN99e
| |--A. ferox Lowe 1833T02
| `--A. paraonai D’Erasmo 1924P93
`--+--EvermannellidaeSN02
| |--Odontostomops normalops (Parr 1928)PN99c
| |--CoccorellaSN02
| | |--C. atlantica (Parr 1928)PN99c
| | `--C. atrata (Alcock 1893)PN99c
| `--EvermannellaSN02
| |--E. ahlstromi Johnson & Glodek 1975S94
| |--E. atrataB96
| |--E. balbo (Risso 1910)S94
| |--E. indica Brauer 1906PN99c
| |--E. megalops Johnson & Glodek 1975PN99c
| `--E. melanoderma Parr 1928 [=E. indica melanoderma]S94
`--ScopelarchidaeSN02
|--Rosenblattichthys alatus (Fourmanoir 1970)PN99a
|--BenthalbellaSN02
| |--B. dentataSN02
| `--B. infans Zugmayer 1911PN99a
|--ScopelarchoidesSN02
| |--S. climax Johnson 1974PN99a
| |--S. danae Johnson 1974PN99a
| `--S. signifer Johnson 1974PN99a
`--ScopelarchusSN02
|--S. analis (Brauer 1902)PN99a
|--S. guentheri Alcock 1896PN99a
|--S. michaelsarsi Koefoed 1955PN99a
`--S. nolfi Steurbaut 1982P93

*Type species of generic name indicated

References

[B-RB13] Betancur-R., R., R. E. Broughton, E. O. Wiley, K. Carpenter, A. López, C. Li, N. I. Holcroft, D. Arcila, M. Sanciangco, J. C. Cureton, II, F. Zhang, T. Buser, M. A. Campbell, J. A. Ballesteros, A. Roa-Varon, S. Willis, W. C. Borden, T. Rowley, P. C. Reneau, D. J. Hough, G. Lu, T. Grande, G. Arratia & G. Ortí. 2013. The tree of life and a new classification of bony fishes. PLoS Currents Tree of Life April 18 2013. doi: 10.1371/currents.tol.53ba26640df0ccaee75bb165c8c26288.

[B96] Bond, C. E. 1996. Biology of Fishes 2nd ed. Saunders College Publishing: Fort Worth.

Davis, M. P., & C. Fielitz. 2010. Estimating divergence times of lizardfishes and their allies (Euteleostei: Aulopiformes) and the timing of deep-sea adaptations. Molecular Phylogenetics and Evolution 57: 1194–1208.

[G01] Günther, A. 1901. A contribution to the history of Plagyodus (Steller). Annals and Magazine of Natural History, series 7, 7: 35–36.

[ND13] Near, T. J., A. Dornburg, R. I. Eytan, B. P. Keck, W. L. Smith, K. L. Kuhn, J. A. Moore, S. A. Price, F. T. Burbrink, M. Friedman & P. C. Wainwright. 2013. Phylogeny and tempo of diversification in the superradiation of spiny-rayed fishes. Proceedings of the National Academy of Sciences of the USA 110 (31): 12738–12743.

[P93] Patterson, C. 1993. Osteichthyes: Teleostei. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 621–656. Chapman & Hall: London.

[PN99a] Paxton, J. R., & V. H. Niem. 1999a. Scopelarchidae. Pearleyes. In: Carpenter, K. E., & V. H. Niem (eds) The Living Marine Resources of the Western Central Pacific vol. 3. Batoid fishes, chimaeras and bony fishes part 1 (Elopidae to Linophrynidae) pp. 1925–1926. FAO: Rome.

[PN99b] Paxton, J. R., & V. H. Niem. 1999b. Anotopteridae. Daggertooth. In: Carpenter, K. E., & V. H. Niem (eds) The Living Marine Resources of the Western Central Pacific vol. 3. Batoid fishes, chimaeras and bony fishes part 1 (Elopidae to Linophrynidae) pp. 1950. FAO: Rome.

[PN99c] Paxton, J. R., & V. H. Niem. 1999c. Evermannellidae. Sabertooth fishes. In: Carpenter, K. E., & V. H. Niem (eds) The Living Marine Resources of the Western Central Pacific vol. 3. Batoid fishes, chimaeras and bony fishes part 1 (Elopidae to Linophrynidae) pp. 1951. FAO: Rome.

[PN99d] Paxton, J. R., & V. H. Niem. 1999d. Omosudidae. Omosudid. In: Carpenter, K. E., & V. H. Niem (eds) The Living Marine Resources of the Western Central Pacific vol. 3. Batoid fishes, chimaeras and bony fishes part 1 (Elopidae to Linophrynidae) pp. 1952. FAO: Rome.

[PN99e] Paxton, J. R., & V. H. Niem. 1999e. Alepisauridae. Lancetfishes. In: Carpenter, K. E., & V. H. Niem (eds) The Living Marine Resources of the Western Central Pacific vol. 3. Batoid fishes, chimaeras and bony fishes part 1 (Elopidae to Linophrynidae) pp. 1953. FAO: Rome.

[SN02] Sato, T., & T. Nakabo. 2002. Paraulopidae and Paraulopus, a new family and genus of aulopiform fishes with revised relationships within the order. Ichthyological Research 49: 25–46.

[S94] Swinney, G. N. 1994. Comments on the Atlantic species of the genus Evermannella (Scopelomorpha, Aulopiformes, Evermannellidae) with a re-evaluation of the status of Evermannella melanoderma. Journal of Fish Biology 44: 809–819.

[T02] Tighe, K. A. 2002. Lancefishes. Family Alepisauridae. In: Collette, B. B., & G. Klein-MacPhee (eds) Bigelow and Schroeder’s Fishes of the Gulf of Maine 3rd ed. pp. 196–197. Smithsonian Institute Press: Washington.

Wassersug, R. J., & R. K. Johnson. 1976. A remarkable pyloric caecum in the evermannellid genus Coccorella with notes on gut structure and function in alepisauroid fishes (Pisces, Myctophiformes). Journal of Zoology 179 (2): 273–289.

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