Rhadinoloricaria macromystax ( Günther, 1869 )

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 : 488-490

Rhadinoloricaria macromystax ( Günther, 1869)

Loricaria macromystax Günther, 1869 , Proceedings of the Zoological Society of London, (pt 2): 426–428, figs. 5–6. Upper

Amazon Rhadinoloricaria macromystax Isbrücker & Nijssen, 1974 , Beaufortia, 22(290):73–74, figs. 1–2. Isbrücker 1980:122; Isbrücker 1981:88; Ortega & Vari 1986:18; Burgess 1989:444; Isbrücker 2001:29, 32; Isbrücker 2002:28;

Ferraris, in Reis et al. 2003:341; Ferraris 2007:293; Barriga S. 2012:112 (references).

Material examined: MEPN 18664, 114.4 mm SL, Ecuador, Provincia Sucumbíos, Río Jivino Negro , afluente del río Napo, 00°15’04”S 76°53’25”W, 15 Dec 2015, G. González .

Diagnosis. Rhadinoloricaria macromystax is distinguished from its only known congener by snout shape wider and more projected (snout length 14.6%–15.1% SL vs. 11.3%–13.3% SL.). Further distinguished by shorter caudal peduncle (postanal length 45.2%–46.1% SL vs. 48.9%–50.8% SL), dorsal-fin closer to caudal-fin (postdorsal length 54.3% SL vs. 57.5%–59.0% SL), and abdomen totally covered with plates (plates loosely connected in our specimen) vs. abdomen partially or totally covered with plates.

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

Head outline, in dorsal view, triangular, anterior apex rounded, sides very slightly concave, almost straight. Snout projected, spatula-shaped, anterior edge rounded ( Figs. 1 , 2 ). 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 the posterior border of orbits to second plate before dorsal-fin origin, keels convergent posteriorly, then parallel or slightly divergent over first two plates; plate before dorsal-fin origin without keel or with very low medial keel ( Fig 1 ). In ventral view of head, tip of snout covered with plates; posteriorly with naked area visible in front of the upper lip. Surface anterior to pectoral-fin girdle and under lower lip naked ( Fig. 2 ).

Abdomen loosely covered with plates. 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, band enlarged with more plates of different sizes, forming patch, ending just in front of anus. Longitudinal medial stripe divides the belly surface into two areas. Over these areas, small, irregular plates disposed laterally and loosely arranged; some solitary surrounded by naked surface. Plates more grouped anteriorly, and more dispersed laterally and posteriorly. Anus surrounded by narrow naked area ( Fig. 1 ). Row with eight to ten lateral plates (thoracic plates) present between bases of pectoral and pelvic-fins, most anterior plate smaller, elliptical, not well projected laterally, remaining seven to nine plates elongated, projected laterally ( Fig. 1 ).

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 with unbranched barbelets. Lower lip broader than the upper, its border with longer barbelets branched; surface covered with barbelets and papillae ( Fig 2 ). Teeth minute, and similar in both jaws; cusp rounded and flat with a very small lateral projection that does not reach distal border. Premaxilla with two or three teeth. Dentary with four or five teeth.

Buccal ornamentation as described for genus. Outer side of premaxillae with three conical barbelets, unbranched, differently sized. Barbelets seem rooted in wide papillae. Inside mouth, just on center and behind premaxillae, there is one thick barbelet, ramified into three or four conical arms, similarly sized and unbranched ( Fig. 2 ).

Lateral body plates 32, 18 coalescent plates (double keeled), 14 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. Caudal-fin i,10,i, unbranched dorsal caudal ray projected as a long filament. Anal-fin i,5, its origin on lateral plate 10. Pectoral-fin i,6, when adpressed, tip of unbranched ray surpassing pelvic-fin origin. Pelvic-fin i,5, distal region of unbranched ray is slightly curved and when adpressed, almost or reaches anal-fin origin. For additional data see Günther (1869) and Isbrücker & Nijssen (1974).

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. 1 ). Dorsally, maxillary barbel with alternating dark (black) and light brown (yellowish) bands ( Fig. 1 ). Laterally, between pelvic and anal fins, five or six black (dark) blotches, irregularly square shaped ( Fig 1 ).Ventral region of head and body whitish or yellowish. Dorsal, pectoral and pelvic fins with rectangular or square black blotches on rays; interradial membranes hyaline. Dorsal, pectoral and pelvic fin spines with four, five and four black blotches, respectively. Anal fin uniformly whitish or yellow. Caudal fin with four black blotches on rays, and two transverse black bands. Anterior transverse band wide and well defined near base of middle rays; posterior band thin and weakly defined. Elongated, dorsal caudal-fin ray, banded dark (black) and light brown or yellowish. Distal border of caudal fin hyaline ( Fig 1 ).

Geographic distribution. Type locality of R. macromystax is upper Amazon River, in Peru, without more details. In Ecuador, the single specimen comes from Jivino Negro River , a tributary of Napo River , Sucumbíos province ( Fig. 6 ). Additionally , two lots with juveniles (not identified at species level) come from localities very near, Aguarico and Jivino rivers ( Fig. 6 ) .

Figures

FIGURE 1. Rhadinoloricaria macromystax, MEPN 18664, 114.4 mm SL. Lateral, dorsal and ventral view, photograph by V. Carvajal.

FIGURE 2. Buccal ornamentation detail in Rhadinoloricaria macromystax, MEPN 18664, 114.4 mm SL.

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.