Rhadinoloricaria stewarti, Provenzano-Rizzi & Barriga-Salazar, 2020

Provenzano-Rizzi, Francisco & Barriga-Salazar, Ramiro, 2020, New finding of Rhadinoloricaria macromystax (Siluriformes: Loricariidae) redescription of the genus and description of a new species from Ecuador, Zootaxa 4779 (4), pp. 485-500 : 491-494

Rhadinoloricaria stewarti , new species

Figures 3 , 4 , 5 Table 1

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Holotype. MEPN 15094, 108.7 mm SL, Ecuador, Orellana Province, Tiguino No. 1 River, tributary of Cononaco River , Napo River system, 150 m from bridge, at military post, approx. 01°01’16”S 76°58’46”W, 11 Feb 1990, R. Barriga.

Paratypes. Ecuador, Pastaza Province: MEPN 10303 , 2 , 109.9 – 125.4 mm SL, Bobonaza River , near its mouth on Pastaza River, approx. 02°22’18”S 76°22’18”W Oct. 1963, M. Olalla. MEPN 14710 , 3 , 107.4 – 118.7 mm SL; Corrientes River, approx. 02°10’50”S 76°40’32”W, May 1964, M. Olalla. MECN-DP- 4247, 110.5 mm SL, Villano River, tributary of Curaray River , Napo River system, approx. 01°23’12”S 76°57’22”W, Oct. 2014, L. Guarderas .

Diagnosis. Rhadinoloricaria stewarti is distinguished from R. macromystax by snout shape, more pointed and less projected (snout length 11.3%–13.3% SL vs. 14.6%–15.1% SL). Further distinguished by longer caudal peduncle (postanal length 48.9%–50.8% SL vs. 45.2%–46.1% SL.), more distance dorsal-fin to caudal-fin (postdorsal length 57.5%–59.0% SL vs. 54.3% SL), and abdomen plating variable, totally or partially covered with plates vs. abdomen totally covered with plates.

Description. Morphometric data given in Table 1. Head and body extremely depressed, principally caudal peduncle. Dorsal profile of body from tip of snout to anterior border of eyes straight and ascendant, then gradually descending straight to caudal-fin origin. Ventral profile of body straight and horizontal. In dorsal view, contour of body straight and convergent posteriorly, tapering gradually. Dorsal surface from the dorsal-fin origin to caudal-fin origin flat. Ventral surface of caudal peduncle flat ( Fig. 3 ).

Head contour (outline), in dorsal view, triangular, anterior apex rounded and sides straight. Snout projected, spatula-shaped, anterior edge rounded ( Figs. 3 , 4 , 5 ). Nares very near eye, and juxtaposed, anterior smaller than posterior. Interorbital space very narrow. Orbit with weak notch at posterior border. Anterior border of orbit raised and with small odontodes. Two low keels run from posterior border of orbits to second plate before dorsal-fin ori- gin, keels converge posteriorly, and then become parallel. In ventral view of head, tip of snout covered with plates; posteriorly with naked area visible in front of the upper lip ( Fig. 3 ). Surface anterior to pectoral-fin girdle and under the lower lip naked.

Abdomen covered with plates in two patterns. At level and over pectoral girdle, transverse band of irregularly arranged plates present. Behind and at center of pectoral girdle, transverse band continues posteriorly as a longitudinal medial row towards anus. At pelvic girdle level, the row enlarges into patch, with more plates of different sizes, ending just in front of anus. Longitudinal medial row divides belly surface into two naked areas, with small plates randomly disposed, generally grouped anteriorly and more dispersed posteriorly ( Fig. 4a ). In other specimens, row composed by one or two small, irregular polygonal plates, and two complete naked areas ( Fig. 4b ). Anus surrounded by naked narrow area. Row with nine to eleven lateral plates between bases of pectoral and pelvic-fins, most anterior two plates smaller and irregularly rounded, not projected laterally, remaining seven to nine elongated plates, projected laterally (true thoracic plates) ( Figs. 3 , 4 ).

Mouth ventral, more or less rounded. Upper lip narrow, its border with barbelets not branched; upper lip surface with barbelets and few papillae. Upper lip border continuous with maxillary barbel. Maxillary barbel very long, surpassing pectoral-fin base, almost reach pelvic-fin origin. Maxillary barbel carry unbranched barbelets along its border. Lower lip broader than upper, its border has longer barbelets branched. Lower lip surface covered with barbelets or with papillae and barbelets ( Figs 4 , 5 ). Presence of many papillae on lower lip correlated with a male sexual dimorphism during the breading season (males carry the eggs in the mouth). Teeth minute and few, similar in both jaws. Teeth small, spoon shaped, with a small lateral projection that does not reach distal margin, cusp rounded. Premaxilla with four teeth. Dentary with six to eight teeth ( Fig. 5 ).

Buccal ornamentation as indicated for genus. Outer side of each premaxilla with four or five conical barbelets, unbranched, differently sized. Barbelets seem rooted in wide papillae. Inside mouth, just on center, and behind premaxillae, with one thick barbelet, branched in three or four conical arms, unbranched, with same or different size ( Fig. 5 ).

Lateral body plates 32–33, 17–18 coalescent plates, and 14–15 lateral plates with single keel. First three lateral plates (posterior to cleithral spine) without keels. Dorsal-fin i,7 its origin located slightly behind pelvic-fin origin. Adipose fin absent. Pectoral-fin i,6, when adpressed, tip of unbranched ray surpassing pelvic-fin origin. Pelvic-fin i,5 distal region of the unbranched ray is slightly curved and when adpressed, almost or reaches anal-fin origin. Anal-fin i,5 its origin on lateral plate 10 or 11. Caudal-fin i,10,i dorsal, unbranched caudal ray projected as long filament ( Fig 3 ).

Color in alcohol. Dorsal surface of head and body yellow or light brown with black (dark) irregular blotches or stripes, disposed and oriented randomly, over snout, mostly arranged longitudinally ( Fig. 3 ). Dorsally, maxillary barbel with alternating dark (black) and light brown (yellowish) bands ( Fig. 3 ). Laterally, between pelvic and anal fins, four to six black (dark) blotches, inverted hairpin-shaped irregularly, discolored in some specimens. Ventral region of head and body whitish. Dorsal, pectoral and pelvic fins with rectangular or square black blotches on rays; interradial membranes hyaline. Dorsal, pectoral and pelvic-fin spines, may have up to eight, six and four black blotches, respectively. Anal fin uniform whitish or yellow. Caudal fin with three or four black blotches on rays, simulating three or four transversal dark bands. Anterior transverse band wide and well defined near base of middle rays; posterior band thin and weakly defined. Distal border of caudal fin hyaline ( Fig. 3 ).

Geographic distribution. Specimens of R. stewarti come from the Napo, Corrientes, and Pastaza rivers, in Orellana and Pastaza provinces, eastern Ecuador ( Fig. 6 ). Apparently, R. stewarti may have a wide geographical distribution, but the few specimens captured suggest is an uncommon species.

Etymology. The specific epithet honors Donald S. Stewart, in recognition of his contributions to the knowledge of the freshwater fishes, especially the Napo River, Ecuador.

Figures

FIGURE 3. Rhadinoloricaria stewarti, MEPN 15094, 108.7 mm SL, holotype. Lateral, dorsal and ventral view, photograph by V. Carvajal.

FIGURE 4. Abdomen covering variation observed in Rhadinoloricaria stewarti. a) MEPN 15094, 108.7 mm SL, holotype. b) MEPN 14710, 114.6 mm SL, paratype.

FIGURE 5. Buccal ornamentation in Rhadinoloricaria stewarti, a) MEPN 15094, 108.7 mm SL, holotype. b) MEPN 14710, 114.6 mm SL, paratype.

FIGURE 6. Map of Ecuador showing the geographic distribution of Rhadinoloricaria macromystax, red square, and Rhadinoloricaria stewarti, type locality, red star, with abdomen almost cover, red triangles, with abdomen partially cover yellow triangles. Rhadinoloricaria sp., juveniles (unidentified), black circles.