Odontocharacidium varii, Rodrigues & Netto-Ferreira, 2020

Rodrigues, Elizabeth Kathleen de Queiroz & Netto-Ferreira, Andre L., 2020, A new miniature species of Odontocharacidium (Characiformes: Crenuchidae) from the Río Orinoco basin, Venezuela, Neotropical Ichthyology 18 (2), pp. 1-11 : 3-7

Odontocharacidium varii , new species

urn:lsid:zoobank.org:act:44171E14-9E40-4960-ACAE-26896C655D3F

( Fig. 1 ; Tab. 1 )

Odontocharacidium aphanes (not Weitzman, Kanazawa, 1977). —Buckup, 1993a:305– 41 (phylogenetic study of Characidiinae). — Buckup, 1993b:136 (description of Odontocharacidium ; distribution). — Buckup, 2003:93 (Checklist; occurrence in Venezuela). — Buckup, van der Sleen, 2018:147 (Field guide; distribution).

Holotype. MHNLS 26156, 14.7 mm SL, Venezuela, Río Negro Municipality , Río Orinoco, Caño Chola , where it crosses the road from San Carlos de Río Negro to Solano, 1°58’00”N 67°00’00”W, 11 Apr 1985, R.P. Vari.

Paratypes. All from Venezuela, Amazonas: ANSP 161317, 8, 14.3–15.8 mm SL, Venezuela, Amazonas, Cano Caño entering eastern side of Río Casiquiare ca. 7.0 km approx. downstream from mouth of Río Pamoni , 2°48’00”N 65°58’00”W, 20 Mar 1987, B. Chernoff, S.W.G. Lopes, J. Fernandez, O. Castillo, M.E Antonio. FMNH 105971, 4, 12.7–12.8 mm SL, Venezuela, Território Federal Amazonas [Currently Estado Amazonas], Caño Curcutito about. 1 km upstream mouth in Río Autana , 4°43’48”N 67°37’12”W, 11 Feb 1992, B. Chernoff, A. Machado-Allison, J. A Wheeler, J. Fernandez, N. M. Gotschall. USNM 270149, 21, 14.1–16.6 mm SL (2 c&s), 14.8–15.8 mm SL, collected with holotype.

Diagnosis. Odontocharacidium varii differs from O. aphanes by the presence of the antorbital (vs. antorbital absent); the presence of the supraorbital laterosensory canal (vs. canal absent); the presence of postcleithrum 1 (vs. postcleithrum 1 absent); the presence of conspicuous bars extending ventrally to the middle portion of the body (vs. bars restricted to the dorsal portion of the body); and the presence of two dark round blotches located at the tip of caudal peduncle (vs. blotches absent).

Description. Morphometric data for the holotype and paratypes, Tab.1 . Body short, relatively compressed. Dorsal profile convex from snout tip to dorsal-fin terminus, slightly concave or nearly straight from that point to insertion of anteriormost dorsal caudal-fin procurrent rays. Ventral profile convex from lower lip to pelvic-fin insertion, moderately convex from that point to anal-fin origin, becoming slightly concave from that point to insertion of first ventral procurrent caudal-fin ray.

Mouth small, terminal. Teeth on both jaws conical, Fig. 2 . Premaxilla with single row of 9(1) or 10(1) teeth decreasing in size laterally. Maxilla reaching vertical through anterior margin of orbit. Maxilla with 9(1) or 10(1) teeth along entire ventral edge, Fig. 2 . Dentary with two series of teeth, outer series with 8(2), inner series with 9(1) or 12(1). Ectopterygoid teeth 6(1) or 7(1). Endopterygoid edentulous. Nostrils round distinctly separated by fleshy bridge without dermal flaps. Posterior nostril closer to orbit and slightly larger than anterior nostril. Small cranial fontanel bordered by supraoccipital, parietal and frontal. Branchiostegal rays 4(2); 3(2) in the anterior ceratohyal, and 1(2) between the anterior ceratohyal and posterior ceratohyal. Antorbital present. Parietal branch of supraorbital laterosensory canal present.

Scales cycloid. Lateral line longitudinal series with 29(1), 30*(5), 31(7), 32(3) or 33(2) scales, of which 4(6), 5*(8) or 6(2) are perforated. Longitudinal series above lateral line 3(18) or 4*(2); and 4*(17) or 5(2) below. Predorsal scales 6(1), 7*(10) or 8(9). Isthmus completely scaled. Circumpeduncular scales 12*(20).

Pectoral-fin total rays 7(1), 8(5) or 9*(14), second and third rays longest. Tip of adpressed pectoral fin not reaching pelvic-fin origin. Postcleitrum 1 present. Pelvic-fin total rays 8(3), 9*(14) or 10(2); first, second and third rays longest. Longest pelvic-fin rays reaching vertical through anal-fin origin. Supraneurals 4(2), anterior to neural spines of vertebral centra 5-8(2). Dorsal-fin rays ii,9*(22); second and third rays longest; first pterygiophore anterior to neural spine of centrum 9(2). Adipose fin present or absent, present in holotype. Anal-fin rays ii,5(5), ii,6*(6) or ii,7(9); third and fourth rays longest; first pterygiophore anterior to haemal spine of centrum 20(1) or 21(1). Caudal-fin principal rays 10/8(1) or 10/9*(21). Hypural 6 present. Precaudal vertebrae 17(2), caudal 15(2); total vertebrae 32(2).

Coloration in alcohol. Background color of head and body pale yellow. Dark brown chromatophores scattered on sides of head. Chromatophores conspicuously concentrated on upper lip, with area between nostrils forming diffuse band. Small concentration of chromatophores from lower lip to near terminus of maxilla. Concentration of chromatophores forming dark triangular suborbital blotch. Dorsal profile of head and posterior margin of orbit with scattered chromatophores forming light brown pigmentation. Dorsal portion of head conspicuously more pigmented than lateral portions. Opercular membrane hyaline.

Humeral blotch present, conspicuous. Vertical bars on dorsal portion of body 6(2), 7(8), 8*(7) or 9(3); bars anterior to insertion of dorsal fin 2*(19) or 3(1); 2*(20) along dorsal-fin base; 3(1), 4*(16) or 5(3) between dorsal-fin terminus and distal tip of caudal peduncle. Bars reaching beyond the midline portion of the body ventrally usually between pelvic-fin and anal-fin origins, with posterior most four bars reaching ventral portion of body. Horizontal septum intermittently pigmented, forming series of thin, dark dashes from pectoral girdle to near tip of caudal peduncle. Ventral portion with concentration of chromatophores on mid-ventral scales forming three thin dark bands at pelvic-fin origin, near anus and at anal-fin base. Caudal peduncle with two dark round blotches at base of each caudal-fin lobe. Pectoral, pelvic, anal and caudal fins hyaline with scattered chromatophores at distal tips. Dorsal fin with concentration of chromatophores forming two discrete horizontal bands, one at middle of in rays and the other at distal tip.

Sexual dimorphism. Dissection of paratypes of Odontocharacidium varii for gonad inspection failed to unambiguously determine sex of available specimens, as gonads of all examined specimens seemed to be immature or in resting stages. Additionally, no distinguishable external secondary sexually dimorphic characters were observed in those specimens.

Geographical distribution. Odontocharacidium varii is known from the upper portion of the Río Orinoco , Fig. 3 .

Etymology. The specific epithet is in honor to Richard P. Vari, first collector of the new species and constant professional inspiration to the authors. A noun in genitive.

Conservation status. Odontocharacidium varii is known from three different localities in the upper Río Orinoco basin. Although none of the sampling sites is within preservation areas, those appear to be well preserved. Besides, there are several national parks and indigenous areas surrounding the known area of occurrence of the species, suggesting the lack of significant threats to the conservation of the species. Therefore, Odontocharacidium varii can be classified herein as a Least Concern ( LC) species according to the International Union for Conservation of Nature ( IUCN) categories and criteria ( IUCN, 2019).

Remarks. Odontocharacidium varii present a slight variation of color pattern, with some specimens having it more pronounced than others. The bands, bars and the humeral blotch can vary in intensity among specimens from the same lot, Fig. 1 . It is unclear at this moment if this phenomenon is indicative of intraspecific variation or coloration fading of the specimens. Nevertheless, both limits of the variation range allow unambiguous distinction between specimens of O. varii from O. aphanes .

Comparative material examined. Brazil, Rio Negro: MZUSP 12978 , 1 , 13.4 mm SL (holotype of Odontocharacidium aphanes Weitzman & Kanazawa, 1977 ). MZUSP 12979 , 3 , 11.4 – 13.0 mm SL (paratypes of Odontocharacidium aphanes ). MZUSP 109657 , 2, 12.3– 11.8 mm SL. MPEG 25491, 2, 14.6–16.2 mm SL. Rio Branco: INPA 39429, 2, 13.1– 12.4 mm SL. MZUSP 113270, 3, 10.1–10.3 mm SL. MZUSP 113665, 36, 10.8– 13.3 mm SL. LBP 15115, 12, 14.1–15.9 mm SL, 1 c&s, 14.6 mm SL. LBP 15114, 8, 15–16.1 mm SL, 1 c&s, 14.7 mm SL.

Figures

FIGURE 1 | Odontocharacidium varii, new species, A. Holotype, MHNLS 26156, 14.7 mm SL, Venezuela, Río Negro Municipality, Río Orinoco; Paratype, USNM 270149, 14.3 mm SL, Venezuela, Río Negro Municipality, Río Orinoco. Scale bar = 1 mm.

FIGURE 2 | Odontocharacidium varii, new species, USNM 270149, paratype, 15.8 mm SL, Venezuela, Río Negro Municipality, Río Orinoco. Lateral view of mandibular arch and dentition, flipped right side, anterior to left.

FIGURE 3 | Map of geographical distribution of Odontocharacidium varii (circles). Type-locality represented by the same symbol in white color.