Gymnotus pantanal Fernandes, Albert, Daniel-Silva, Lopes, Crampton and de Almeida-Toledo, 2005

Craig, Jack M., Malabarba, Luiz R., Crampton, William G. R. & Albert, James S., 2018, Revision of Banded Knifefishes of the Gymnotus carapo and G. tigre clades (Gymnotidae Gymnotiformes) from the Southern Neotropics, Zootaxa 4379 (1), pp. 47-73 : 63-64

Gymnotus pantanal Fernandes, Albert, Daniel-Silva, Lopes, Crampton and de Almeida-Toledo, 2005

Figure 13, Table 1

Material examined: Argentina: MACN-ict 9655 (19), 154–257 mm, Corrientes, Río Paraná drainage, Esteros del Riachuelo (27°34’39”S, 058°15’23”W). Brazil, Mato Grosso do Sul: MZUSP 67874 (holotype), 196 mm, Río Miranda , near Miranda (20°11’78”S, 056°30’13”W) ; MZUSP 67875 (paratype), 189 mm, Rio Paraguarí (18°59’81”S, 057°39’24”W) ; MZUSP 67875 , 192 mm, same locality as MZUSP 67875 ; MZUSP 67876 , 251 mm, same locality as MZUSP 67875 ; NUP 4554 (5), 195–235 mm, upper Rio Paraná drainage, marginal lagoons of Rio Paraná (24°05’33”S, 054°15’17”W); NUP 6044 (2), 152–204 mm, Água Queçaba stream; NUP 7934, 152 mm, upper Rio Paraná drainage, Rio Paracaí (23°39’30”S, 053°55’10”W); NUP 9290 (17), 139–260 mm, same locality as NUP 9311; NUP 9311 (5), 168–210 mm, upper Rio Paraná drainage, Rio Marreco, Jacutinga stream (24°42’56”S, 053°46’21”W); NUP 9312 (11), 113–248 mm, upper Rio Paraná drainage, Rio Toledo, Pinheirinho stream (24°44’05”S, 053°42’55”W) ; UFRGS 11910 , Corumbá, Rio Paraguai drainage, Rio Miranda or Aquidauna between Corumbá and Aquidauna (23°22’47”S, 052°30’07”W) . Paraguay: NRM 42830, 240 mm , Caaguazu, Río Paraná drainage, arroyo crossing Rt. 2 West of J. E. Estringarriba (25°22’40”S, 055°42’32’W”); UMMZ 206080 (21), 82–260 mm , Paraguarí, Río Paraguay drainage, Arroyo in Parque Nacional Ybycui (26°58’00”S, 057°19’60”W).

Diagnosis. Gymnotus pantanal differs from all sympatric members of the G. carapo clade on the following characters: 1, a short head (HL 7.4%–11.7%, mean 8.9% TL vs. 9.7%–14.1%, mean 11.7% TL); 2, a wide head (HW 62.2–76.8% HL, mean 69.8% HL vs. 46.2%–71.9% HL, mean 61.5% HL); 3, many precaudal vertebrae (PCV 37–38, mode 37 vs. 31–34, mode 32); 4, many pored lateral-line scales anterior to the first ventral lateral-line ramus (PLR 45–50, median 47 vs. 23–47, median 37). Gymnotus pantanal also differs from other Gymnotus on its color pattern, characterized by 21–24, mode 22 dark bands, four times as wide as pale anteriorly and forming inverted Y -shapes posteriorly, with pale bands never extending above lateral line on anterior half of body, and anterior 80% of dorsum with very faint or absent banding.

Description: Morphometric and meristic data in Table 1. Sexually monomorphic, including in breeding condition. Total length to 251 mm. Morphological maturity at roughly 110 mm. Scales rounded to slightly ovoid, present on entire postcranial portion of body. Gape large in mature specimens, to or beyond posterior nares. Mouth superior with lower jaw longer than upper, rictus decurved. Chin fleshy and protuberant with fleshy pad of electrosensitive organs overlying tip of snout and oral jaws. Anterior narial pore partially to entirely included within gape in narial fold. Anterior nares large, subequal to eye diameter. Circumorbital series ovoid. Ethmoid region broad between anterior nares, with rounded anterior margin. Eye position lateral, lower margin of eye dorsal or horizontal to rictus. Premaxilla with 13–16 (mode 15) teeth disposed in two rows along outer margin, arrowhead shaped anteriorly, conical posteriorly. Curved median margin of premaxilla. Maxilla-palatine articulation near anterior tip of endopterygoid. Maxilla vertical, rod-shaped, narrow distally with a straight ventral margin, length equal to roughly width of 4–6 dentary teeth. Dentary with one row of 26–28 (mode 28) teeth, 7 arrow-head shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abut at midlength. Dentary posteroventral process shorter than posterodorsal, narrow distally. Dentary ventral margin lamella narrow, depth less than posterior process. Opercle dorsal margin straight to slightly convex. Dorsal opercular process lamellar or rugose, crest absent or small, posterior margin entirely smooth, without spines or processes. Preopercle with anteroventral notch, posterodorsal laterosensory ramus with two superficial pores, margin of medial shelf entire, median shelf large, more than one-half width of symplectic. Metapterygoid superior and inferior portions approximately equal in size, ascending process robust, long, base equal in length, curved, tip simple. Interopercle dorsal margin ascending process broad. Subopercle dorsal margin concave. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin square. Anguloarticular process long, extending beyond ventral margin of dentary. Mandible long, extended, length greater than twice depth. Trigeminal nerve canals connected within the hyomandibula. Posterior lateral line fenestra contacting posterodorsal margin of hyomandibula. Cranial fontanels closed in juveniles and adults. Frontal shape broad, width at fourth infraorbital greater than that of parietal, anterior margin of straight, continuous with margins of adjacent roofing bones, postorbital process broad, more than two times width of supraorbital canal. Lateral ethmoid absent. Parietal rectangular, length less than width. Parasphenoid anteroventral portion reduced, extending dorsal to lateral margin of parasphenoid, posterior processes narrow. Prootic foraminae combined for cranial nerves Vp and V2–3 +VII. Adductor mandibula muscle undivided at insertion, intermuscular bones absent. All basibranchials unossified. Gill rakers not contacting gill bar. Pectoral with 14–18 (mode 15) rays, medial radial large. Mesocoracoid broad, length more than four times width.

Cleithrum narrow, ventral margin curved, anterior limb long, more than 1.8 times ascending limb, deeply incised on its anteroventral margin, without large facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity of moderate length, with 37–38 (mode 37) precaudal vertebrae. Rib five robust along its entire extent, less than three times width of rib six. Hemal spines present. Displaced hemal spines absent. Length anal-fin pterygiophores equal to or longer than hemal spines. Anal fin with 131–280 (median 184) rays. Lateral line ventral rami 19–23 (median 20). Caudal appendage short, less one-half length of pectoral fin. Single hypaxial electric organ along entire ventral margin of body. Three rows of electroplates near caudal insertion of anal fin.

Color in Alcohol: Bands irregular in shape, width and color, on specimens and among individuals. Ground color dark, chocolate brown. Anterior 80% of dorsum with very faint or absent banding in specimens of all sizes. Juveniles (TL <150 mm) and most adults with obliquely-oriented, thin cream-colored bands with wavy, irregular margins ventrolaterally located between tail tip and pectoral-fin base (21–24 mode 22). Dark bands chocolatebrown in color, four times as wide as pale anteriorly and forming inverted Y -shapes posteriorly. Pale bands infrequently branched, and never extend above lateral line on anterior half of body. Interband contrast greatest in juveniles and ventrally to caudally in adults. Head never banded, spotted, or blotched, dark grey dorsally grading to lighter grey ventrally. Numerous chromophores speckled over branchiostegal membranes and ventral surface of head. Pectoral-fin rays brown, interradial membranes hyaline. Anterior 80% of anal fin membrane dark brown, gray or black, posterior 20% translucent.