Rhinotocinclus polyochrus (Schaefer, 1988), 2022

Reis, Roberto E. & Lehmann A., Pablo, 2022, A new genus of armored catfish (Siluriformes: Loricariidae) from the Greater Amazon, with a review of the species and description of five new species, Neotropical Ichthyology (e 220002) 20 (2), pp. 1-100 : 30-32

Rhinotocinclus polyochrus (Schaefer, 1988) , new combination

( Fig. 19 ; Tab. 3 )

Parotocinclus polyochrus Schaefer, 1988:184 (Type-locality: Venezuela, Território Federal Amazonas, Depto. Río Negro, Río Mawarinuma tributary at Neblina base camp, on right bank of riffle; 00°55’N 66°10’W, elevation 120 m. Holotype: AMNH 74482).

Diagnosis. Rhinotocinclus polyochrus is distinguished from R. acuen , R. bockmanni , R. chromodontus , R. dani , R. dinizae , R. hera , R. jumaorum , R. pentakelis , R. marginalis n. sp., and R. loxochelis n. sp. by possessing an adipose fin (vs. adipose fin absent), and by having a Y-shaped light mark from the snout tip to each nostril (vs. light mark V-shaped or present as two separate lines from snout tip diverging to each nostril). It is distinguished from R. collinsae , R. halbolthi , and R. hardmanni by lacking accessory teeth on both premaxilla and dentary (Figs. 5B,C; vs. accessory teeth present); the odontodes on the ventral surface of first pelvic-fin ray bent and pointing mesially (Fig. 9A; vs. odontodes aligned with main ray axis, Fig. 9B); a triangular dark spot on the anterior portion of the dorsal-fin membrane (Fig. 8B; vs. dorsal-fin spot absent); a Y-shaped light mark from snout tip to nostrils (vs. Y-shaped light mark absent); and a larger orbit, 26.3–28.7% snout length (vs. orbit 18.9–24.6% snout length). Rhinotocinclus polyochrus is distinguished from R. britskii and R. kwarup , by having the snout more acutely pointed (Fig. 11B; vs. snout more broadly rounded, Fig. 11A); dark bars on body wider and closer together (Fig. 7B; vs. dark bars on body narrower and more widely spaced, Fig. 7A); and 2 plates between the posterior border of the rostral plate and the nostril (Fig. 12A; vs. one plate). Rhinotocinclus polyochrus is distinguished from R. eppleyi and R. longirostris by having 3–4 irregular series of middle abdominal plates (vs. 4–5 irregular series); and dark bars on body 1+2 fused (vs. dark bars on body separated). It is distinguished from R. variola , R. yaka , R. discolor n. sp., R. isabelae n. sp., and R. pilosus n. sp. by having a conspicuous light bar in front of dorsal fin, extended on head as a Y-shaped mark towards each nostril (vs. bar and Y-shaped mark on head absent). It is further distinguished from P. variola and R. yaka by having fewer premaxillary teeth (23–32 vs. 33–51 and 34–39, respectively); from R. discolor n. sp. and R. pilosus n. sp. by having smaller eye (38.9–40.6% interorbital distance vs. 52.1–63.7% and 45.7–55.2%, respectively); and from R. isabelae n. sp. by having a shallower caudal peduncle (6.8–7.1% SL vs. 8.1–8.8% SL) and 3–4 lateral abdominal plates (vs. 1–2 lateral abdominal plates).

Geographical distribution. Rhinotocinclus polyochrus is only known from the type-locality in the Río Mawarinuma, at the Neblina Ridge in the state of Amazonas, Venezuela ( Fig. 15 ). The Río Mawarinuma is a tributary to the Río Baria which empties in the Casiquiare Canal, which drains to the upper Negro.

Remarks. Rhinotocinclus polyochrus is most similar to R. longirostris and R. eppleyi , from which it is distinguished by having 3–4 irregular series of middle abdominal plates, while R. longirostris and R. eppleyi have 4–5 series, and by having dark bars 1+2 fused on body, versus all bars separated. Coincidently, R. polyochrus and R. longirostris were described in the same year (Schaefer, 1988 and Garavello, 1988, respectively) and both authors were apparently unaware of the description of the other species, as they were not compared in either description. Unfortunately, R. polyochrus is only known from the type-material, the holotype and one paratype, both being females. Rhinotocinclus polyochrus , listed as Parotocinclus polyochrus , is currently assessed as Least Concern (LC) by the IUCN.

Material examined. AMNH 74482 , holotype (measured ), AMNH 77520 , 1 paratype (measured), creek tributary to Río Mawarinuma at Neblina base camp , Amazonas, Venezuela, approx. 00°55’N 66°10’W .

Figures

FIGURE 15 | Geographical distribution of Rhinotocinclus species of the R. britskii group in central and northwestern South America. Rhinotocinclus britskii (white dots); R. discolor n. sp. (purple dots); R. eppleyi (orange dots); R. isabelae n. sp. (pink dots); R. kwarup (red dots); R. longirostris (blue dots); R. pilosus n. sp. (yellow dots); R. polyochrus (cyan dot); R. variola (black dots); R. yaka (light green dots). T = Type-locality; T1 = type-locality of Parotocinclus britskii, T2 = type-locality of P. amazonensis, T3 = type-locality of P. aripuanensis.

FIGURE 19 | Rhinotocinclus polyochrus, holotype, AMNH 74482, 27.6 mm SL, female, creek tributary to Río Mawarinuma at Neblina base camp, Amazonas, Venezuela.