Gymnotus eyra, Craig & Correa-Roldán & Ortega & Crampton & Albert, 2018

Craig, Jack M., Correa-Roldán, Vanessa, Ortega, Hernán, Crampton, William G. R. & Albert, James S., 2018, Revision of Gymnotus (Gymnotiformes: Gymnotidae) from the Upper Madeira Basin of Bolivia and Peru, with descriptions of two new species, Zootaxa 4413 (1), pp. 111-132 : 122-125

Gymnotus eyra n. sp.

Figure 6D , Table 2

Holotype: MUSM 60276 , 122 , Peru, Madre de Dios, Manu, Cuenca Río Los Amigos , Aguajal cicra Pozo Pedro (12°33.611’S, 070°06.593’W), coll. By Max Hidalgo, 05/07/2002.

Paratypes: MUSM 21404 (5), 51–119, same date and locality as MUSM 60276.

Nontypes: Bolivia, Beni: AUM 23644, 152 mm TL, Rio Beni, Rio Madeira drainage, 26 km SSW of Riberalta (11°07’00”S, 066°11’00”W) ; INHS 37119 (5), 94–176 mm TL, Rio Beni, Rio Madeira drainage, Cuneta (borrow pit) 3 km E Estac. (14°47’32.28”S, 066°12’59.69”W) . Peru, Madre de Dios: MUSM 14021 , 185 mm TL, Manu, Rio Madre de Dios, Quebrada Pachija (11°57’S, 071°17’W) ; MUSM 19993 (2), 132–148 mm TL, Manu, Rio Madre de Dios, Los Amigos, Aguajal (12°33’00”S, 070°00’36”W) ; MUSM 2 1388 (6), 67–132 mm TL, Cuenca Rio Los Amigos , cerca Aguajal, Pozo Pedro (12°33’00”S, 070°06’00”W) ; MUSM 21778 , 147 mm TL, Madre de Dios, Tambopata, Cuenca Río Madre de Dios, Aguajal , Aguas Negras, Pozo Santa Elena . Peru, Cusco: MUSM 36141 (2), 199–254 mm TL, La Convención, Echarate, Rio Urubamba Basin , Rio Parotori , Quebrada Piriabindeni (11°46’59.88”S, 073°05’60.00”W).

Diagnosis: Gymnotus eyra is morphologically similar to G. mamiraua , but differs on the following characters: one, fewer pectoral-fin rays (P1R 10–13, mode 11 vs. 12–16, mode 15 in G. mamiraua ); two, fewer ventral lateralline rami (VLR 10–15, mode 13 vs. 16–18, median 17 in G. mamiraua ). Gymnotus eyra further differs from other members of the G. carapo clade from the Upper Madeira ( G. c. madeirensis , G. chaviro and G. riberalta ) on the following characters: one, a color pattern (shared with G. mamiraua ) consisting of pale bands narrow, less than one third width of dark bands, sharp band margins, and pale bands extending to dorsal mid-line; two, few, larger scales over the anal-fin pterygiophores (APS six to eight, mode seven vs. eight to 13, mode 12 in other G. carapo clade from the Upper Madeira); three, few pored lateral-line scales before the first ventral lateral-line ramus (PLR 30–41, median 39 vs. 40–61, median 50 in other G. carapo clade from the Upper Madeira). Gymnotus eyra further differs from other members of the G. carapo clade throughout the Neotropics in possessing a color pattern (similar to G. mamiraua ) consisting of pale bands less than one fifth width of dark bands, sharp band margins, and pale bands extending to dorsal mid-line vs. bands interrupted into patches anterodorsally, with silver, blue or green metallic countershading on dorsum of adults of G. arapaima , dark bands lost in large adults (> 250 mm TL) of G. ardilai , small, rounded dark spots over entire body except posterior 20% of some specimens of G. bahianus , bands faint or absent in all specimens of G. chimarrao , one to three inverted Y -shaped dark bands posteriorly and pale bands not reaching above lateral line in anterior two thirds of body of G. choco , bands faint or absent from 80% of dorsum in all specimens, and narrow pale bands (less than one fifth width of dark bands) which never extend above lateral line on anterior half of body in G. pantanal , pale bands wider than dark bands in G. sylvius , narrow pale interbands (less than one third width of dark bands) extending above lateral line and often to dorsal midline in G. ucamara .

Description: Sexually monomorphic. Size up to 185 mm TL with adult body proportions attained at about 110 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 55%. Body profile slender, body depth 85.4–114.5% total length. Head length moderate, 9.6–12.3% total length. Snout length moderate, 32.0– 40.0% head length. Mouth width narrow, 30.9–43.9% head length. Preanal distance long, 61.3–84.5% head length. Anal-fin long, 78.5–84.4% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage. Scales above lateral line intermediate, four to six, mode 5. Scales over anal-fin pterygiophores large, with six to eight, mode seven rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with 16 teeth disposed in single row along outer margin. 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 15 teeth, four to five arrowhead shaped anteriorly. Dentary posteroventral process nearly as long as posterodorsal, narrow distally. Dentary ventral margin lamella narrow, depth less than posterior process. Dentary anteroventral margin rounded in lateral view, without a hook. Mandible long, extended, length greater than twice depth. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin square. Metapterygoid superior and inferior portions approximately equal in size, ascending process robust, long, base shorter than length, curved, tip complex. Hyomandibular trigeminal canals connected. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Posterior lateral line fenestra contacting posterodorsal margin of hyomandibula. Preopercle with anteroventral notch, posterodorsal laterosensory ramus with two superficial pores, margin of medial shelf entire, median shelf large, more than half width of symplectic. Interopercle dorsal margin ascending process broad. Opercle dorsal margin straight to slightly convex, its posterior margin smooth. Opercular posterior margin entirely smooth. Subopercle dorsal margin concave. Cranial fontanels closed in juveniles and adults. Frontal shape broad, width at fourth infraorbital less 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 unossified. Parietal rectangular, length less than width. Parasphenoid anteroventral portion robust, extending ventral to lateral margin of parasphenoid, posterior processes narrow. Prootic foramen Vp separate from V2-3 +VII. Adductor mandibula undivided at insertion, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.

Cleithrum narrow, ventral margin straight, anterior limb short, less than one-point-eight 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 34 precaudal vertebrae (n=1). Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Length anal-fin pterygiophores equal to or longer than hemal spines. Pectoral fin narrow, with 10–13 rays, mode 11. Anal fin of moderate length, with 167–227 rays, median 193. Lateral-line variable, with 10–15 ventral rami, median 12. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with three rows of electroplates near caudal insertion of anal fin.

Color in alcohol: Body ground color dark, chocolate brown. Bands variable in number among individuals and in shape and arrangement within individuals, uncorrelated with sex. Adults (TL> 110 mm TL) with 16–23 (mode 20, n=16) obliquely-oriented, thin cream-colored bands located between tail tip and pectoral-fin base on lateral surface and onto dorsum, more regular in juveniles. Pale bands regular, sinuous and undivided, with sharp contrast between margins and ground color. Dark bands chocolate-brown in color, three times as wide as pale anteriorly, similar in width dorsoventrally, and wider caudally. Head chocolate-brown dorsally and on operculum, grading to lighter brown ventrally and on snout. Posteroventrally-oriented band at nape connected to anteriormost anteroventral pale band of body in many specimens. Pectoral and anal fins with dark rays and inter-radial membranes. Anal fin with pale zone caudally.

Etymology: Specific epithet derived from to the jaguarundi ( Herpailurus yagouaroundi ), the red form of which is locally known as the “ eyra ”. The convention of naming Gymnotus for felids, which are often similarly nocturnal, predatory, banded or spotted, is shared with G. pantherinus , G. tigre and G. onca . Noun in apposition.

Habitats: Gymnotus eyra usually inhabits slowly-moving channels (caños) on forested floodplains, aguajales of the palm Mauritia flexuosa , and seasonally flooded savannahs, and is less commonly found in small, upland (non-floodplain) forest streams (quebradas).

Figures

FIGURE 6. All five valid Gymnotus species from the Upper Madeira Basin, Bolivia and Peru. Scale bars = 10 mm TL. A. Gymnotus carapo madeirensis holotype, UMSS 06964, 178 mm TL. B. Gymnotus chaviro holotype, MUSM 33715, 233 mm TL. C. Gymnotus coropinae, MUSM 20264, 118 mm TL. D. Gymnotus eyra n. sp., INHS 37119, 178 mm TL. E. Gymnotus riberalta n. sp. holotype,CBF 10248, 199 mm TL.