Eigenmannia robsoni, 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 : 14-19

Eigenmannia robsoni , new species

urn:lsid:zoobank.org:act:A0CD04E8-6A7A-49B0-8D9A-580B8A7B85D0

( Figs. 3E, F , 6 ; Tab. 1 )

Eigenmannia virescens (non Valenciennes, 1836). —Fowler, 1941:196 (listed, Rio Parnahyba, Therezina, Piauhy). —Silva et al., 2015:5 (listed, ichthyofauna of the Gurgueia River). —Melo et al., 2016:374 (listed, ichthyofauna of lower Parnaíba River).

Eigenmannia macrops (non Boulenger, 1897). —Ramos et al., 2014:4 (listed, ichthyofauna of the Parnaíba River basin).

Holotype. MZUSP 125872, 139.3 mm LEA, rio Parnaíba , Muricí dos Portelas, Piauí, 03°18’24.8”S 42°05’36.2”W, T. Ramos & S. Ramos, 10 Apr 2010 .

Paratypes. All from Brazil, rio Parnaíba basin : UFPB 8204 , 4 +1 CS, 121.3–130.8 mm LEA, collected with holotype . MZUSP 74875 , 2 , 83.8–100.2 mm LEA, rio Poti near the Parque Municipal da Floresta Fóssil, Teresina , Piauí, 05°05’14.5”S 42°47’19.4”W, M. de Pinna, 16 Nov 2001 . MZUSP 87481 , 1, 201.8 mm LEA, ribeirão Jenipapo, Balsas , Maranhão, 07°26’18”S 46°11’47”W, A. Akama & E. Baena, 23 Mar 2005 . UFPB 8201 , 5 , 86.6–109.5 mm LEA, rio Parnaíba at Community of Beira Rio, Buriti , Maranhão, 03°54’06.9”S 42°43’27.8”W , T. Ramos & S. Ramos, 9 Apr 2010 . UFPB 8202 , 7 +1 CS, 88.4–134.5 mm LEA, rio Parnaíba, Magalhães de Almeida , Maranhão, 03°18’24.8”S 42°05’36.0”W , T. Ramos & S. Ramos, 10 Apr 2010 . UFPB 10014 , 1, 122.8 mm LEA, rio Gurgueia, Cristiano Castro , Piauí, 08°48’55.7”S 44°13’47.9”W, W. Severi et al., 22 Jun 2006 .

Non-types. MZUSP 5110 , 1, 203.9 mm LEA, Teresina Market , Expedição do Departamento de Zoologia, 19 Jun 1966 . MZUSP 97958 , 1 , not measured, Isle at Lagoa de Parnaguá , Parnaguá, Piauí, 10°14’41”S 44°38’50”W, O. Oyakawa, A. Akama , V. Garutti & J. Nolasco, 8 Apr 2001 . MZUSP 98596 , 1 , 21.2 mm LEA, Rio Balsas , Balsas, Maranhão, 07°32’13”S 46°02’20”W, O. Oyakawa, A. Akama , V. Garutti & J. Nolasco, 6 Apr 2001 . UFPB 8196 , 4 , 82.2–128.3 mm LEA, Rio Parnaíba , Ribeiro Gonçalves, Piauí, 07°33’24”S 45°14’58”W , T. Ramos & S. Ramos, 3 Apr 2010 . UFPB 8197 , 1 , 54.0 mm LEA, rio Parnaíba , Ribeiro Gonçalves, Maranhão, 07°33’07”S 45°14’18” W , T. Ramos & S. Ramos, 3 Apr 2010 . UFPB 8198 , 2 , 55.15–92.3 mm LEA, rio Parnaíba , Benedito Leite, Piauí, 07°14’43”S 44°34’16”W , T. Ramos & S. Ramos, 4 Apr 2010 . UFPB 8199 , 4 , 76.8–198.6 mm LEA, rio Parnaíba , Uruçuí, Piauí, 07°14’22”S 44°34’08”W , T. Ramos & S. Ramos, 4 Apr 2010 . UFPB 8200 , 4 , 59.0– 126.2 mm LEA, Rio Parnaíba , village of Correntes , Caxias, Maranhão, 04°33’42”S 42°52’01”W , T. Ramos & S. Ramos, 8 Apr 2010 . UFPB 11899 , 1 , 57.8 mm LEA, Riacho Nova Brasília , stream tributary of Santo Antônio , village of Nova Brasília , rod. PI-113, Cabeceiras do Piauí, Piauí, 04°27’14”S 42°18’47”W, W. Severi & E. França, 18 Jun 2006 . UFPB 11900 , 4 , 166.1 – 225.1 mm LEA, Mercado Público , União, Piauí, 04°35’24”S 42°52’31”W , T. Ramos , 24 Sep 2009 . UFPB 11901 , 21 , 75.2–154.3 mm LEA, rio Gurguéia , Jurumenha, Piauí, 07º04’36”S 43º30’54”W, W. Severi & E. França, 7 Apr 2005 . UFPB 11902 , 2 , 113.4 – 134.5 mm LEA, Barragem Boa Esperança , São João dos Patos, Maranhão, 06°39’29”S 43°42’34”W , T. Ramos , R. Ramos & G. Moro, 3 Feb 2009 . UFPB 11903 , 2 , 143.3 – 203.4 mm LEA, rio Parnaíba , Benedito Leite, Maranhão, 07°14’09”S 44°34’24”W, W. Severi & E. França, 1 Apr 2005 . UFPB 11904 , 7 , 77.5–134.3 mm LEA, rio Parnaíba , Alto Parnaíba, Maranhão, 09°06’52”S 45°55’35”W , T. Ramos & S. Ramos, 1 Apr 2010 . UFPB 11905 , 1 , 92.3 mm LEA, rio Canindé , Francisco Aires, Piauí, 06°37’28.7”S 42°41’43”W , T. Ramos, G. Moro & M. Silva, 19 Sep 2009 . UFPB 11907 , 1 , 64.4 mm LEA, rio Parnaíba , Uruçuí, Piauí, 07°14’11”S 44°34’03”W, W. Severi & E. França, 1 Apr 2005 . UFPB 11908 , 2 , 72.8–108.4 mm LEA, rio Uruçui-Preto , PI-247/BR-324, Uruçuí, Piauí, 07°23’19”S 44°36’42”W, W. Severi & E. França, 31 Mar 2005 . UFPB 11909 , 1, 138.3 mm LEA, rio Parnaíba , Alto Parnaíba, Maranhão, 09°06’53”S 45°55’37”W , T. Ramos & S. Ramos, 6 Feb 2009 . UFPB 11910 , 1, 122.1 mm LEA, rio Parnaíba , village of Beira-Rio , Buriti, Maranhão, 03°53’39”S 42°43’25”W , T. Ramos & S. Ramos, 17 Apr 2011 . UFPB 11911 , 1, 121.1 mm LEA, rio Parnaíba , village of Beira-rio , Buriti, Maranhão, 03°53’39”S 42°43’25”W , T. Ramos & S. Ramos, 17 Apr 2011 . UFPB 11912 , 5 , 82.5–153.4 mm LEA, rio Parnaíba , União, Piauí, 04°34’27”S 42°52’13”W , T. Ramos & S. Ramos, 18 Apr 2011 . UFPB 11913 , 3 , 71.2–97.7 mm LEA, rio Parnaíba , village of Manga , Barão do Grajaú, Maranhão, 06°14’47”S 42°51’24”W , T. Ramos & S. Ramos, 18 Apr 2011 . UFPB 11914 , 1, 115.9 mm LEA, rio Parnaíba , Murici dos Portelas, Piauí, 03°18’24”S 42°05’36”W , T. Ramos & S. Ramos, 16 Apr 2011 . UFPB 11915 , 37 , 61.2–97.9 mm LEA, rio Longá , Nossa Senhora de Nazaré, Piauí, 04°40’20”S 42°13’W , T. Ramos & S. Ramos, 23 Jun 2011 . UFPB 11921 , 2 , 86.1–95.1 mm LEA, rio Titara , Cocal de Telha, Piauí, 04°39’39”S 42°03’41.7”W , T. Ramos, S. Costa, Y. Rocha & L. Neto, 8 Dec 2018 .

Diagnosis. Eigenmannia robsoni , 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 (16.2–21.3% HL vs. 26.4–29.7% HL), and the presence of a short caudal filament (19.9–36.4 % LEA vs. 67.5–79.3% LEA). The new species differs from all other species of the E. trilineata species-group, except E. besouro , E. bumba , E. correntes , E. dutrai , E. guchereauae , E. meeki , E. oradens , E. sirius , E. vicentespeleaea , E. virescens , and E. waiwai by the subterminal mouth (vs. terminal). Eigenmannia robsoni differs from aforementioned species by the following combination of characters: (1) absence of the lateral line stripe (vs. presence in E. besouro , E. correntes , E. dutrai , E. guchereauae , E. meeki , E. oradens , E. sirius , E. vicentespelaea , and E. waiwai ); (2) absence of superior midlateral stripe (vs. presence in E. besouro , E. bumba , E. correntes , E. dutrai , E. sirius , and E. vicentespeleaea ); (3) 182–228 anal-fin rays (vs. 143–154 in E. correntes ); (4) 12–15 scales rows above lateral line (vs. 7–10 in E. besouro , 8–11 in E. oradens , 7–8 in E. vicentespelaea , 9–11 in E. virescens , and 9–10 in E. waiwai ); (5) 107–131 scales on lateral line (vs. 140–168 in E. meeki ), (6) 32–34 premaxillary teeth (vs. 19–23 in E. bumba , 11–20 in E. correntes , 75 in E. guchereauae , 38–42 in E. oradens , 15–24 in E. sirius , 25–26 in E. vicentespeleaea , and 22 in E. virescens ); (7) 35–44 dentary teeth (vs. 19–30 in E. besouro , 20–29 in E. bumba , 16–18 in E. correntes , 88 in E. guchereauae , and 21–23 in E. meeki ); (8) 9–12 endopterygoid teeth (vs. 13–15 in E. meeki , 14–17 in E. waiwai ); (9) depth of posterodorsal expansion on infraorbitals 1+2 half as long as infraorbitals 1+2 length (vs. as long as infraorbitals 1+2 length in E. dutrai , E. guchereauae , E. oradens , E. sirius ); (10) basibranchial 1 unossified (vs. ossified in E. virescens ); (11) 13 precaudal vertebrae (vs. 15 in E. meeki and E. sirius ); (12) coronomeckelian bone length corresponding to 20% of length of Meckel’s cartilage (vs. 45% in E. oradens and E. waiwai ).

Description. Body shape and pigmentation shown in Fig. 6 , morphometric data in Tab. 1 . Largest examined specimen 225.1 mm LEA. Body elongate and distinctly compressed laterally. 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 nearly straight from tip of lower jaw to vertical through tip of pectoral fin and concave from this point to anal-fin terminus. Caudal filament short (19.9–36.4% LEA).

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 nearly straight from tip of lower jaw to isthmus. Snout pointed in lateral view. Mouth subterminal. Mouth rictus at vertical through a point between anterior and posterior nares or vertical through posterior nostril. 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 between middle and 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 middle of opercle to vertical through posterior margin of eye. Urogenital papilla usually not developed in specimens under 111 mm LEA. Branchial membranes joined at isthmus. Gill rakers on first branchial arch 12(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*(8), 14(5), or 15(4). Anterior most perforated lateral-line scale along vertical through pectoral-fin origin. Lateral-line scales to vertical through base of last anal-fin ray 107–131(N = 17), 126 in holotype.

Pectoral-fin rays ii,12(2), ii,13(1), ii,14(14), or ii,15*(2). Distal pectoral-fin margin straight. Total anal-fin rays 182–228(N = 17), 216 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 32(1) or 34(1) in five rows ( Fig. 3E ). Dentary teeth 35(1), or 44(1) in three(2) rows ( Fig. 3F ). Dentary teeth not increasing in size along dentigerous surface. Coronomeckelian bone length near 20% Meckel’s cartilage length. Endopterygoid teeth nine(1) or 12(1) in one(1) or three(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 five(2). Upper pharyngeal teeth eight(1). Lower pharyngeal teeth 12(1). Precaudal vertebrae 13(1). Transitional vertebrae three(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. 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 forming stripe-like pattern on anal-fin base. Anal-fin base stripe approximately half as wide as orbital diameter. Head covered by dark chromatophores, more concentrated on opercular region. Pectoral and anal fins hyaline with scattered dark chromatophores overlying fin rays.

Geographical distribution. Eigenmannia robsoni is widespread in the rio Parnaíba basin, Northeastern Brazil. This species occurs in the main course of rio Parnaíba, and in its tributaries rio Balsas, rio Gurgueia, rio Longá, rio Piauí-Canindé, and rio Poti ( Fig. 4 ).

Ecological notes. Eigenmannia robsoni is recorded in perennial and intermittent rivers with clear and lentic waters, sandy substrate with lots of aquatic vegetation. In perennial rivers, the riparian vegetation is typical of the Cerrado, with palms of the species Mauritia flexuosa . In contrast, in intermittent rivers, the riparian vegetation is the “fringe forests”, dominated by palm trees such as Copernicia prunifera .

Etymology. The epithet “ robsoni ” is in honor of Robson Tamar da Costa Ramos, ichthyologist, for his contributions to studies of the Caatinga ecoregion, especially in the Parnaíba river basin. A patronym.

Conservation status. Eigenmannia robsoni 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, being widespread in 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).

Remarks. Eigenmannia robsoni was initially identified as E. macrops by Ramos et al.

(2014). Such identification was based on the lack of lateral stripes, which are also absent in E. macrops. However, E. robsoni can be readily diagnosed from E. macrops as described in the diagnosis.

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 6 | Eigenmannia robsoni, MZUSP 125872, holotype, 139.3 mm LEA, rio Parnaíba, Muricí dos Portelas, Piauí, 03°18’24.8”S 42°05’36.2”W. A. lateral view of head, B. lateral view of body.