 |
| Eigenmannia sirius
Peixoto & Ohara, 2019
|
Abstract
A new species of Eigenmannia is described from the rio Mutum, tributary of upper rio Juruena, rio Tapajós basin, Comodoro, Mato Grosso, Brazil. The new species is distinguished from all congeners by coloration pattern, position of the mouth, number of scales rows above lateral line, number of premaxillary and dentary teeth, number of precaudal vertebrae, orbital diameter, mouth width, relative depth of posterodorsal expansion on infraorbitals 1+2 and relative size of coronomeckelian bone. Comments on potentially useful characters in phylogenetic studies derived from musculature, discussion on Eigenmannia species-group and the first dichotomous key for Eigenmannia are provided.
 |
| Fig 1. Lateral view of Eigenmannia sirius, MZSUP 121668, holotype, 127.5 mm LEA, Mato Grosso, Brazil, rio Mutum, tributary of rio Juruena, rio Tapajós basin. |
 |
| Fig 5. Color in life of Eigenmannia sirius, MZUSP 123938, paratypes, 93.7 and 77.3 mm LEA, A and B respectively, rio Mutum, rio Juruena, Mato Grosso, Brazil. Caudal filament damaged. |
Eigenmannia sirius, sp. nov.
Diagnosis: Eigenmannia sirius is diagnosed from all putative congeners with exception of Eigenmannia trilineata species-group (sensu [Peixoto, et al., 2015]), by the presence of superior midlateral stripe (vs. absence). The new species differs from all species of the Eigenmannia trilineata species-group, except E. besouro, E. correntes, E. vicentespelaea, and E. waiwai, by the subterminal mouth (vs. terminal). It differs from E. besouro, E. correntes, E. vicentespelaea, and E. waiwai by relative depth of posterodorsal expansion on infraorbitals 1+2 corresponding to 70% length of infraorbitals 1+2 (Fig 2—vs. 40% in E. besouro, E. correntes and E. waiwai, and approximately equals total length of infraorbitals 1+2 in E. vicentespelaea), and in having 15 precaudal vertebrae (vs. 14 in E. besouro and E. correntes, 13–14 in E. vicentespelaea and 12–13 in E. waiwai). Eigenmannia sirius can be differentiated from E. besouro by the origin of the superior midlateral stripe at vertical between base of 23rd to 31st anal-fin ray (vs. origin at vertical between 5th to 15th anal-fin ray). The new species is also diagnosed from E. correntes by the eye diameter (17.2–23.8% HL vs. 10.6–13.3% HL), and by the mouth width (13.1–22.4% HL vs. 23.5–26.0% HL). Eigenmannia sirius is further distinguished from E. vicentespelaea and E. waiwai by having 15–24 premaxillary teeth (Fig 3A vs. 25–26 and 35–40, respectively) and 15–33 dentary teeth (Fig 3B vs. 38–45 and 37–38, respectively). It additionally differs from E. vicentespealea by having 9–12 scale rows above lateral line (vs. seven or eight) and the coronomeckelian bone corresponding to 20–25% of length of Meckel’s cartilage (Fig 3B vs. 45%). The new species can be distinguished from Archolaemus species by the eye completely covered by thin membrane (vs. a free orbital rim); from Distocyclus by the rounded snout in profile (vs. conical snout); from Japigny by the absence of alternating dark bands on flanks (vs. presence); and from Rhabdolichops by the region above the lateral line on the anterior portion of the body covered by scales (vs. absence of scales above the lateral line on the anterior portion of the body).
Etymology: The specific epithet sirius is an allusion to the alpha star of the Canis Major constellation that represents the state of Mato Grosso in the Brazilian national flag, a reference of the state of occurrence of the new taxon. A noun in apposition.
 |
| Fig 10. Photograph of rio Mutum, type locality of Eigenmannia sirius, illustrating habitat. |
Distribution and habitat: Eigenmannia sirius is currently known only from rio Mutum, a tributary of the upper rio Juruena, rio Tapajós basin, Comodoro, Mato Grosso, Brazil (Fig 9). The type-locality is 502 m above sea level at the Chapada dos Parecis plateau. It is a clearwater river up to c. 3–6 m wide and 0.5–2.5 m deep, preserved riparian vegetation, swift current, and sand, pebbles and dead leaves on the bottom (Fig 10). Several types of microenvironment were sampled exhaustively, but E. sirius was captured only between root and subaquatic vegetation. Other species sampled syntopically were Aequidens cf. rondoni (Miranda Ribeiro), Erythrinus erythrinus (Bloch & Schneider), Hemigrammus skolioplatus Bertaco & Carvalho, Hyphessobrycon hexastichos Bertaco & Carvalho, H. melanostichos Carvalho & Bertaco, Hasemania nambiquara Bertaco & Malabarba, and Hoplerythrinus unitaeniatus (Spix & Agassiz). No other Gymnotiformes were collected with E. sirius.
Luiz Antônio Wanderley Peixoto and Willian M. Ohara. 2019. A New Species of Eigenmannia Jordan & Evermann (Gymnotiformes: Sternopygidae) from rio Tapajós, Brazil, with Discussion on Its Species Group and the Myology within Eigenmanniinae. PLoS ONE. 14(8): e0220287. DOI: 10.1371/journal.pone.0220287
