Eigenmannia cacuria, Dutra & Ramos & Menezes, 2022

Dutra, Guilherme Moreira, Ramos, Telton Pedro Anselmo & Menezes, Naércio Aquino, 2022, Description of three new species of Eigenmannia (Gymnotiformes: Sternopygidae) from the rio Mearim and rio Parnaíba basins, Northeastern Brazil, Neotropical Ichthyology (e 210117) 20 (1), pp. 1-23 : 11-14

Eigenmannia cacuria , new species

urn:lsid:zoobank.org:act:CE0B94F3-2259-45F0-88C9-99BA81B3992C

( Figs. 3C, D , 5 ; Tab. 1 )

Eigenmannia virescens (non Valenciennes, 1836). —Ramos et al., 2014:4 (listed, ichthyofauna of the Parnaíba River basin).

Holotype. MZUSP 125871 , 110.0 mm LEA, riacho Enxada, Alto Parnaíba , Maranhão, 08°51’21”S 45°59’14”W, O. Oyakawa, A. Akama, V. Garutti & J. Nolasco, 6 Apr 2001 .

Paratypes. MZUSP 98583 , 4 +1 CS, 53.6–134.0 mm LEA, collected with holotype . UFPB 11916 , 3 +1 CS, 68.4–90.2 mm LEA, Brejo do Boi , Sambaíba, Maranhão, 06°57’54.3”S 45°22’38.2”W, W. Severi & E. França, 6 Apr 2005 .

Non-types. LBP 5572 , 10 , not measured, stream tributary of rio Parnaíba , Santa Filomena, Piauí, 09°09’51”S 45°51’15”W, C. Oliveira & R. Benine , 28 Nov 2007 . UFPB 11896 , 2 , 55.5–117.5 mm LEA, Brejo do Boi , stream tributary of rio Bois , Sambaíba, Maranhão, 06°57’54”S 45°22’38”W, W. Sereri & E. França, 6 Apr 2005 . UFPB 11897 , 5 , 40.9–63.8 mm LEA, rio Parnaíba , under the bridge of BR-321, Ribeiro Gonçalves, Piauí, 07°33’07.6”S 45°14’13.3”W, W. Sereri & E. França, 31 Mar 2005 . UFPB 11898 , 2 , 53.2–70.4 mm LEA, Riacho Volta , PI-247/BR-324, Uruçuí, Piauí, 07°24’16”S 44°50’31”W, W. Sereri & E. França, 31 Mar 2005 . UFPB 11906 , 1 , 73.5 mm LEA, stream tributary of rio Aldeia , MA-006/BR-330, Balsas, Maranhão, 07°43’50”S 46°02’26”W, W. Sereri & E. França, 3 Apr 2005 .

Diagnosis. Eigenmannia cacuria , a member of the E. trilineata species-group, differs from the E. humboldtii species-group by the anal-fin hyaline (vs. anal-fin margin distinctly darkened), and from E. macrops by the absence of enlarged eye (17.5–21.1% HL vs. 26.4– 29.7% HL), and the presence of a short caudal filament (26.4–41.3% LEA vs. 67.5–79.3% LEA). Within the E. trilineata species-group, the new species is diagnosed from all species of the E. trilineata species-group, except E. antonioi Peixoto, Dutra & Wosiacki, 2015 , E. camposi Herrera-Collazos, Galindo-Cuervo, Maldonado-Ocampo & Ríncon-Sandoval, 2020 , E. desantanai Peixoto, Dutra & Wosiacki, 2015 , E. guairaca Peixoto, Dutra & Wosiacki, 2015 , E. lorenata Waltz & Albert, 2018 , E. magoi Herrera-Collazos, Galindo-Cuervo, Maldonado-Ocampo & Ríncon-Sandoval, 2020 , E. matintapereira Peixoto, Dutra & Wosiacki, 2015 , E. microstoma (Reinhardt, 1852) , E. muirapinima Peixoto, Dutra & Wosiacki, 2015 , E. pavulagem Peixoto, Dutra & Wosiacki, 2015 , E. sayona Peixoto & Waltz, 2017 , E. trilineata López & Castello, 1966 , and E. zenuensis Herrera-Collazos, Galindo-Cuervo, Maldonado-Ocampo & Ríncon-Sandoval, 2020 by having a terminal mouth (vs. subterminal). Eigenmannia cacuria differs from the aforementioned species, by the following combination of characters: (1) lateral line stripe restricted to last two-thirds of body (vs. lateral line stripe extending from first perforated lateral line scale to distal portion of caudal filament in E. camposi , E. muirapinima , E. zenuensis ); (2) ii,11–13 pectoral-fin rays (vs. ii, 16–17 in E. matintapereira , and ii, 14–15 in E. trilineata ); (3) 180– 196 anal-fin rays (vs. 216–222 in E. matintapereira , and 198–217 in E. sayona ); (4) 12–15 scales rows above lateral line (vs. 8–10 in E. antonioi and E. desantanai , 9–11 in E. guairaca and E. sayona , 7–10 in E. camposi , and 7–9 in E. zenuensis ); (5) 10–14 premaxillary teeth (vs. 27 in E. camposi , 24–25 in E. desantanai , 32 in E. magoi , 22–24 in E. matintapereira , 16 in E. microstoma , 17 in E. sayona , 31–33 in E. trilineata , and 31–34 in E. zenuensis ); (6) 15–21 dentary teeth (vs. 35–39 in E. magoi , 25–27 in E. matintapereira , and 56–60 in E. zenuensis ); (7) 8–10 endopterygoid teeth (vs. 14–15 in E. desantanai , 5–6 in E. guairaca , 6–7 in E. loretana , 11 in E. magoi , 11–16 in E. microstoma , and 16–17 in E. trilineata ); (8) dentary teeth increasing in size along dentigerous surface (vs. all dentary teeth similar in size in E. desantanai , E. guairaca , E. matintapereira , E. microstoma , E. pavulagem , and E. trilineata ); (9) basibranchial 1 unossified (vs. ossified in E. sayona ); and (10) 14 precaudal vertebrae (vs. 11–12 in E. desantanai , and 15 in E. guairaca ).

Description. Body shape and pigmentation shown in Fig. 5 , morphometric data in Tab. 1 . Largest examined specimen 134.0 mm LEA. Body elongate and distinctly compressed. Greatest body depth at vertical crossing distal tip of pectoral fin. Dorsal profile of body slightly convex from snout tip to vertical through anal-fin terminus. Ventral profile of body convex from tip of lower jaw to vertical through tip of pectoral fin and concave from this point to anal-fin terminus. Caudal filament short.

Head laterally compressed; greatest width at opercular region, greatest depth at nape. Dorsal profile of head convex from snout tip to nape. Ventral profile of head convex from tip of lower jaw to isthmus. Snout round in lateral view. Mouth terminal. Mouth rictus at vertical through anterior nostril or between nares. Anterior nostril tube-like; closer to snout tip than to anterior margin of eye. Posterior nostril round, not tubular, closer to anterior margin of eye than to snout tip, at horizontal line above dorsal margin of eye. Eye small, circular, completely covered by skin, on anterior one-half of HL, laterally oriented. Anus adjacent to urogenital papilla, shifting ontogenetically from vertical through posterior margin of opercle to vertical through posterior margin of eye. Urogenital papilla not developed in specimens under 76 mm LEA. Branchial membranes joined at isthmus. Gill rakers on first branchial arch 13(1).

Scales cycloid and small, extending from posterior most part of head to vertical through tip of caudal filament, present on mid-dorsal region of body. Scales above lateral line at vertical through end of pectoral fin 12(1), 13(4), 14(3), or 15*(1). Anterior most perforated lateral-line scale along vertical through pectoral-fin origin. Lateral-line scales to vertical through base of last anal-fin ray 112–132(N = 9), 127 in holotype.

Pectoral-fin rays ii,11(3), ii,12*(6), or ii,13(1). Distal pectoral-fin margin rounded. Total anal-fin rays 180–196(N = 9), 182 in holotype. Anal-fin origin along vertical through pectoral-fin insertion or slightly posterior. Distal margin of anal fin slightly convex. First unbranched rays tiny, subsequent rays progressively increasing in size toward first branched rays. Branched rays of nearly equal length except for posterior most rays that progressively decrease in length.

Relevant osteological features. Premaxillary teeth 10(1) or 14(1) in two(2) rows ( Fig. 3C ). Dentary teeth 15(1), or 21(1) in two(2) rows ( Fig. 3D ). Dentary teeth increasing in size along dentigerous surface. Coronomeckelian bone length near 20% Meckel’s cartilage length. Endopterygoid teeth eight(1), or 10(1) in one(1) or two(1) rows. Antorbital and infraorbitals 1 to 4 enlarged, partially cylindrical with slender osseous arches. Fifth and sixth infraorbitals slender and tubular. Depth of posterodorsal expansion on infraorbitals 1+2 half as long as infraorbitals 1+2 length. Branchiostegals four(1) or five(1). Upper pharyngeal teeth nine(1). Lower pharyngeal teeth nine(1). Precaudal vertebrae 14(1). Transitional vertebrae five(1). Pleural ribs seven(1). Displaced hemal spines three(1).

Coloration in alcohol. Body ground coloration cream. Body with two layers of chromatophores. Outer layer covered by dark chromatophores gradually more spaced ventrally, more concentrated on perforated scales forming a lateral line stripe, and between lateral line stripe and anal pterygiophores forming a superior midlateral stripe. Lateral line stripe restricted to last two thirds of body. Superior medial stripe fainted, covering the space equivalent to two scales vertically, tapering from vertical through end of body cavity to vertical through to posterior one-third of LEA. Inner layer of pigmentation formed by multiple, small bars of dark chromatophores situated between the musculature associated with anal-fin pterygiophores. Dark individual bars in combination form two stripes-like patterns. Inferior midlateral stripe fainted approximately half as wide as orbital diameter. Anal-fin base stripe approximately half as wide as orbital diameter. Head covered by dark chromatophores. Pectoral and anal fins hyaline with scattered dark chromatophores overlying fin rays.

Geographical distribution. Eigenmannia cacuria is only known from the upper Rio Parnaíba basin, Northeastern Brazil. It occurs in the main course of Rio Parnaíba, and in small streams tributaries of Rio Balsas, the largest tributary of the basin ( Fig. 4 ).

Ecological notes. Eigenmannia cacuria is apparently restricted to perennial rivers. Specimens were collected in a lentic environment, with clear water, sandy substrate, and varying amounts of remnants of riparian vegetation typical of the Cerrado biome, with palms of the species Mauritia flexuosa .

Etymology. The epithet “ cacuria ” is in reference to the “ cacuriá ”, a typical dance in the state of Maranhão, where the holotype was collected. A noun in apposition.

Conservation status. Eigenmannia cacuria apparently does not match any of the extinction risk categories giving by the International Union for Conservation of Nature ( IUCN). The species possesses a relatively broad distribution, occurring at the upper portion of the Rio Parnaíba basin. Therefore, according with the currently available data, and using the criteria of the IUCN Standards and Petitions Subcommittee ( IUCN, 2019), we propose that the species should be classified as Least Concern ( LC). However, we draw attention to the low number of known specimens of this species in a relatively well sampled region.

Figures

FIGURE 3 | Osteological elements of Eigenmannia bumba, MZUSP 123709: A. Premaxillae, B. Lower jaw; Eigenmannia cacuria, UFPB 11916: C. Premaxillae, D. Lower jaw; and Eigenmannia robsoni, UFPB 8202: E. Premaxillae, F. Lower jaw.

FIGURE 4 | Map of Northern Brazil showing distribution of Eigenmannia bumba (white), Eigenmannia cacuria (black), and E. robsoni (red). A star indicates the type locality.

FIGURE 5 | Eigenmannia cacuria, MZUSP 125871, holotype, 110.0 mm LEA, riacho Enxada, Alto Parnaíba, Maranhão, 08°51’21”S 45°59’14”W. A. lateral view of head, B. lateral view of body.