Gymnotus chaviro Maxime & Albert, 2009

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 : 118-119

Gymnotus chaviro Maxime & Albert, 2009

Figure 6B , Table 1

Diagnosis: Gymnotus chaviro differs from all sympatric members of the G. carapo clade on a color pattern consisting of 17–29 (mode 20, n=100) dark gray bands with irregular, wavy margins approximately as wide as pale interbands, 2–3 of the anteriormost five pale interbands with both margins crescent-shaped vs. margins of anteriormost interbands straight or curved in parallel in the G. carapo clade of the Upper Madeira.

Description: Sexually monomorphic. Size up to 275 mm TL with adult body proportions attained at about 120 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 77%. Head length moderate, 8.8–11.7% total length. Snout length moderate, 31.4–39.8% head length. Mouth width intermediate, 35.5–57.8% head length. Preanal distance long, 67.8–99.4% head length. Anal-fin long, 76.5–84.3% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage. Scales above lateral line intermediate, five to nine, mode eight. Scales over anal-fin pterygiophores large, with 12–13, mode 12 rows. Gape small, never extending 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, pipe shaped. Anterior nares small, its diameter four to five times less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with 14 teeth in two rows, and curved median 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 seven to nine dentary teeth. Dentary with 14 arrowhead-shaped teeth anteriorly in outer row and 10 in an anterior inner tooth patch. Posterodorsal and posteroventral dentary processes abut at midlength. Dentary posteroventral process shorter than posterodorsal, narrow distally. Dentary ventral margin lamella wide, depth greater than posterior process. Dentary anteroventral margin rounded in lateral view, without a hook. Mandible long, extended, length greater than twice depth. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin square. Anguloarticular process long, extending beyond ventral margin of dentary. Metapterygoid superior and inferior portions approximately equal in size, ascending process robust, long, base shorter than length, curved, tip simple. 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. Subopercle dorsal margin concave. Opercle dorsal margin straight to slightly convex, its posterior margin smooth. Opercular posterior margin entirely smooth. 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 narrow, less 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 long, more 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 35–38 precaudal vertebrae, mode=37, n=4. 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 large, with 16–19 rays, mode 19. Anal fin long, with 212–280 rays, mode 270. Lateral-line variable, seven to 23 ventral rami, mode eight. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with four 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> 90 mm TL) with 17–29 (mode 20, n=100) oblique pigment gray bands with irregular, wavy margins on lateral surface extending from nape and pectoral-fin base to tip of caudal appendage, oriented vertically to obliquely in an antero-ventral to postero-dorsal diagonal. Dark bands approximately as wide as pale interbands, thinner anteriorly. Majority of dark bands paired with pale intraband. Most bands poorly divided with no sharp contrast; intraband formed by less density of pigments at the middle of the band. Greatest pigment density at band margins, sharper caudally. Three to four dark bands meet at ventral midline anterior to anal-fin origin. Two to three of the anteriormost five pale interbands crescent-shaped. Bands above lateral line continuous on anterior half of body, not visible against ground color at dorsal midline. More regularly-arrayed pigment bands, sharper contrast in juveniles. Head never banded, characterized by dense speckling dorsally fading to pale yellow ventrally. Pectoral and anal fins with uniform light gray rays and interradial membranes. Anal fin with pale zone caudally.

Materials Examined : Peru, Madre de Dios: MUSM 1406 , 127 mm TL, Parque Nacional Manú, Quebrada Pakitza, Aguajal ; MUSM 1759 (2), 142–150 mm TL, Puerto Maldonado, river near Tambopata, Cochachica; MUSM 21405, 138 mm TL; MUSM 22731 (10), 143–210 mm TL, Madre de Dios drainage ; MUSM 16662 , 325 mm TL, Tambopata, Madre de Dios drainage, Lago Copamanu . Peru, Ucayali: MUSM 33715 (holotype), 233 mm TL, Alto Yuruá, Quebrada Dos y medio, small terra firme stream ~two km NW of Breu (09°31’10.50”S, 072°45’45.30”W) ; MUSM 33714 (40, paratypes), 95–275 mm TL, same locality as MUSM 33715 ; FMNH 118274 (10, paratypes), 134–179 mm TL, same locality as MUSM 33715 ; CAS 227893 (10, paratypes), 123–150 mm TL, same locality as MUSM 33715 ; MCZ 168419 (10, paratypes), 115–160 mm TL, same locality as MUSM 33715 ; MCP 43880 (10, paratypes), 116–164 mm TL, same locality as MUSM 33715 ; MZUSP 103035 (10, paratypes), 130–217 mm TL, same locality as MUSM 33715 ; AMNH 248884 (10, paratypes), 104–180 mm TL, same locality as MUSM 33715 .

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.