New species of Curimatopsis from the río Caroni, Orinoco basin, Venezuela, with comments on C. macrolepis (Characiformes: Curimatidae)

A new species of Curimatopsis is described from the highlands of the western Guiana Shield in the río Carapo and río Paragua, tributaries of the río Caroni in the Orinoco basin, southeastern Venezuela. The new species belongs to the Curimatopsis macrolepis clade due to its possession of a long lower jaw that projects past the anterior margin of the upper jaw, and separate first and second hypurals. The new species is diagnosed from remaining species of the Curimatopsis macrolepis clade by having a small-sized inconspicuous dark spot on the midlateral surface of the caudal peduncle, by details of body and fin pigmentation, and by additional morphometric characters. The distribution of C. macrolepis in the Amazon and Orinoco basins is updated based on the examination of museum specimens. Coloration in alcohol. Ground coloration tan to yellowish. Upper lip, snout, and dorsal portion of head and opercle with small, dark chromatophores; lower jaw with field of dark chromatophores, more so along margin of lower lip. Margins of scales along lateral, dorsolateral, and dorsal surface of body outlined by series of small dark chromatophores, but not forming a clear reticulate pattern; more diffuse pattern of small chromatophores on dorsal and dorsolateral regions of body. Dark pigmentation absent on scales over lateral surface and ventral region of the body. Thin-lying dusky stripe along midlateral surface of body from vertical through dorsal-fin origin to caudal peduncle. Dark concentration of chromatophores covering posterior midlateral scales and anterior portions of middle caudal-fin rays. Rays of dorsal, caudal, and anal fins distinctly outlined by small, dark chromatophores. Pectoral and pelvic fins with scattered, small, dark chromatophores. Adipose fin hyaline with small chromatophores concentrated on distal margin. AMNH USNM 226880, 21.2–27.6 mm MZUSP 15974, 26.2–29.6 mm SL, MZUSP 15976, paratypes, 34.5–34.6 mm SL. Curimatopsis evelynae Colombia: USNM 198644, holotype, 22.3 mm SL, USNM 198638, 27.6 mm SL, AMNH 43099, paratypes, 30.7–33.0 mm SL. Curimatopsis guaporensis : Brazil: MZUSP 121189, holotype, 24.0 mm SL, DZSJRP 19418, 20.3–25.7 mm SL, LBP 22725, paratypes, 4, 19.9–24.7 mm SL. Curimatopsis jaci : Brazil: MZUSP 121197, holotype, 28.1 mm SL, LBP 22726, 1, paratype, 31.2 mm SL, MZUSP 118861, paratypes, 4, 28.3–31.3 mm Curimatopsis macrolepis : Venezuela: AMNH 45092, 1, 29.2 mm SL, AMNH 74564, 6, 48.6–61.7 mm SL, AMNH 74565, 6, 32.4–38.2 mm SL, MZUSP USNM 226910, 1, 31.9 mm SL, USNM 226911, 28.0–28.3 mm SL, USNM 226975,

Curimatopsis is supported by 16 synapomorphies (Vari, 1982(Vari, , 1989 and can be diagnosed by the distinctly rounded anterior margin of the maxilla, the absence of the laterosensory canal segment in the first infraorbital, and a reduced laterosensory system on the body, with pores restricted to only the anterior portion thereof (Vari, 1982(Vari, , 1989. Two main clades of Curimatopsis are well defined by morphological and molecular evidence: the C. macrolepis clade supported by three anatomical synapomorphies and the C. evelynae clade supported by five such synapomorphies (Vari, 1982(Vari, , 1989Melo et al., 2018). Five species are assigned to each clade distributed along lowlands of the Orinoco, Amazon, and Paraguay river basins, and coastal Atlantic rivers from the Guianas to northeastern Brazil (Vari, 1982;Melo, Oliveira, 2017;Dutra et al., 2018).
One species of each clade occurs in the Orinoco basin: Curimatopsis macrolepis (Steindachner, 1876), which is also distributed along the Amazon basin (type-locality: Tabatinga, rio Solimões), and C. evelynae Géry, 1964, which also occurs along the rio Negro downstream to Manaus (type locality: río Manacacías, río Meta) (Steindachner, 1876;Géry, 1964;Vari, 1982). At the time of the last revision (Vari, 1982), only a few records of both species were available in museum collections. Subsequent field collections showed that some species, such as C. macrolepis, have broader distributions than originally documented by Vari (1982). Here, a new species of Curimatopsis collected in tributaries of the río Caroni of the Orinoco basin is formally described and updated information on the distribution of C. macrolepis is provided based on examination of museum specimens.

MATERIAL AND METHODS
Counts and measurements follow Vari (1982) and Melo et al. (2016a). Measurements are point-to-point linear distances taken with digital calipers to a precision of 0.1 mm. In the description, parentheses indicate the number of examined specimens for a particular count and an asterisk designates the value for the holotype. Radiographs (rd) were obtained for the holotype and 16 paratypes. Fused PU1+U1 is considered a single bone, and the vertebrae associated with the Weberian apparatus are counted as four elements. Curimatopsis microlepis Eigenmann, Eigenmann, 1889, was originally hypothesized as a member of the C. macrolepis clade (Vari, 1982) Diagnosis. Curimatopsis sabana belongs to the C. macrolepis clade (C. jaci Melo, Oliveira, 2017, C. maculosa Melo, Vari, Oliveira, 2016, C. macrolepis, and C. melanura Dutra, Melo, Netto-Ferreira, 2018 and can be easily diagnosed from species of the C. evelynae clade (C. cryptica Vari, 1982, C. evelynae, C. guaporensis Melo, Oliveira, 2017, C. myersi Vari, 1982, and C. pallida Melo, Oliveira, 2017 by having a longer lower jaw that projects past the anterior margin of the upper jaw (vs. lower jaw shorter and not overlapping the upper jaw), and by separate (vs. fused) first and second hypurals. Within the C. macrolepis clade, C. sabana is diagnosed from C. melanura by the absence (vs. presence) of the dark pigmentation on the entire lower lobe of the caudal fin. It differs from C. jaci by the absence (vs. presence) of a distinctly reticulate color pattern on the flanks of females. It is diagnosed from C. maculosa by the possession of a round 4/12 scielo.br/ni | sbi.bio.br/ni spot of black pigmentation, sometimes very faint, on the midlateral surface of the caudal peduncle (vs. a small posteriorly pointed spot overlapping the posterior midlateral scales), by the absence (vs. presence) of a gap of two or three scales separating the pigmentation of the midlateral stripe and the dark spot on caudal peduncle, by a deeper body, 34.1-39.9% of SL (vs. 26.0-31.6% of SL), and deeper caudal peduncle, 13.7-17.4% of SL (vs. 9.0-13.7% of SL). It differs from C. macrolepis by the possession of a circular and weakly pigmented spot on the caudal peduncle (vs. horizontally elongated and strongly pigmented dark spot on caudal peduncle). Finally, it differs from C. microlepis by 26-28 (vs. 57-63) scales in the longitudinal series from the supracleithrum to the hypural joint.
Description. Morphometric data in Tab. 1. Body relatively short. Dorsal profile of head slightly convex from tip of snout to dorsal-fin origin; gradually descending and nearly straight from dorsal-fin origin to adipose-fin origin and then gently concave to origin of anterior dorsal caudal-fin procurrent ray. Ventral profile more or less evenly convex from chin to terminus of anal-fin base, then gently concave to origin of anterior ventral procurrent ray of caudal fin. Prepelvic region somewhat flattened transversely. Postpelvic region of body transversely rounded.  Head profile acutely triangular with bluntly pointed snout. Lower jaw longer than and projecting past the anterior to limit of upper jaw. Mouth subsuperior, horizontally aligned with center of orbit. Nostrils close; anterior nostrils circular to ovoid, posterior nostrils crescent-shaped with aperture not closed by thin flap of skin separating nares. Adipose eyelid slightly developed anterior to orbit.
Dorsal fin pointed, with distal margin straight and first and second branched rays longest. Distal margin of pectoral fin pointed. Tip of adpressed pectoral fin reaches three or four scales short of vertical through pelvic-fin origin. Pelvic fin profile slightly rounded. Tip of adpressed pelvic fin reaches two to four scales short of anal-fin origin. Caudal fin forked in females and middle caudal-fin rays elongated in males. Adipose fin present. Anal fin emarginate, anterior branched rays one-third length of ultimate ray. Tip of adpressed anal fin reaches two scales short of origin of ventral caudal-fin ray.

Coloration in alcohol.
Ground coloration tan to yellowish. Upper lip, snout, and dorsal portion of head and opercle with small, dark chromatophores; lower jaw with field of dark chromatophores, more so along margin of lower lip. Margins of scales along lateral, dorsolateral, and dorsal surface of body outlined by series of small dark chromatophores, but not forming a clear reticulate pattern; more diffuse pattern of small chromatophores on dorsal and dorsolateral regions of body. Dark pigmentation absent on scales over lateral surface and ventral region of the body. Thin-lying dusky stripe along midlateral surface of body from vertical through dorsal-fin origin to caudal peduncle. Dark concentration of chromatophores covering posterior midlateral scales and anterior portions of middle caudal-fin rays. Rays of dorsal, caudal, and anal fins distinctly outlined by small, dark chromatophores. Pectoral and pelvic fins with scattered, small, dark chromatophores. Adipose fin hyaline with small chromatophores concentrated on distal margin.

Sexual dimorphism.
Only one male specimen (AUM 36458) was identified by its pronounced sexual dimorphism that is typical of species of Curimatopsis (Vari, 1982). The specimen has a deeper caudal peduncle (17.4% of SL) than females (13.7-16.2% of SL), slightly elongate middle caudal-fin rays, and a clear enlargement of the penultimate principal ray of the caudal-fin lower lobe. These features are consistent with other species of Curimatopsis presenting sexual dimorphism (Vari, 1982;Melo, Oliveira, 2017).
Distribution. Curimatopsis sabana is only known from the Carapo and Paragua rivers, which are tributaries of the río Caroni, itself a right-bank tributary of the río Orinoco basin, in the western Guiana Shield in Venezuela (Fig. 2). Various specimens were collected in the region of the río Carapo, near Cerro Guaiquinima (4 km along the river, 300-310 m asl), and one specimen was collected in a drying pool of the lower río Paragua (272 m asl) (Fig. 3). The distribution suggests that C. sabana is restricted to higher elevations of the western Guiana Shield.
Etymology. The specific name sabana refers to the Gran Sabana, a major ecoregion in the western Guiana Shield of southeastern Venezuela, which encompasses the río Caroni basin. A noun in apposition.

Conservation status. Based on Armbruster, Taphorn (2013) who described
Neblinichthys peniculatus from the río Carapo, the type locality of Curimatopsis sabana, the region is sparsely populated and difficult to access, which suggests a lack of significant threats for the species. In addition, another relatively recent expedition found one male specimen in the lower río Paragua, increasing the extent of the known occurrence for the species. Although the species lives in a relatively small area of occurrence, this factor alone does not qualify it for a threatened status. Given the available information, C. sabana is herein recommended to be categorized as Least Concern (LC) under the categories and criteria of the International Union for Conservation Nature (IUCN Standards and Petitions Subcommittee, 2019).

DISCUSSION
Curimatopsis sabana is hypothesized to be a member of the C. macrolepis clade on the basis of one synapomorphy: the possession of an elongate lower jaw that projects past the anterior margin of the upper jaw (Vari, 1982(Vari, , 1989. In addition, the species has the first and second hypurals separated, and the third hypural separated from the autogenous plate of the first and second hypurals. The alternative conditions with first and second hypurals fused and a connection of the third hypural with the autogenous plate represent synapomorphies of the C. evelynae clade (Vari, 1982(Vari, : figs. 1-4, 1989. Relationships within the C. macrolepis clade are still unclear although a recent molecular study (Melo et al., 2016b) provided a hypothesis in which a cryptic species referred to C. macrolepis (rio Negro) represents the earliest split, followed by C. maculosa (rio Tapajós), and three other lineages of C. macrolepis corresponding to the Juruá, Madeira, and Nanay river basins, respectively. Ongoing research using genomic data also suggests that the distinctive C. microlepis, described from Jatuarana along the rio Amazonas below Manaus, does not belong to the C. macrolepis clade, and further research aim to redescribe and clarify the phylogenetic position of the species (Melo et al., unpublished).
Prior to this study, two species of Curimatopsis were known to occur in the Orinoco basin, one for each clade: C. evelynae, a very distinctive species of the C. evelynae clade, and C. macrolepis, described from Tabatinga, rio Solimões at the border of Brazil and Colombia (Steindachner, 1876). Vari (1982) examined five lots of C. macrolepis (AMNH 45092, USNM 226911, USNM 226975, USNM 226976, and USNM 226910) from the main río Orinoco, downriver of Caicara, in the Venezuelan states of Monagas and Delta Amacuro (Vari, 1982: fig. 12). Those specimens along with others from the Orinoco examined here, possess a densely pigmented, horizontally elongate spot on the caudal peduncle, a unique pattern within the C. macrolepis clade (Vari, 1982), and clearly distinct from that of C. sabana (Fig. 4). In fact, no other species in the clade possess such a densely pigmented spot on the caudal peduncle (Melo et al., 2016a;Melo, Oliveira, 2017;Dutra et al., 2018) suggesting that such pattern can be used as a diagnostic feature of C. macrolepis stricto sensu.