A new species of Microglanis ( Siluriformes : Pseudopimelodidae ) from the upper rio Tocantins basin , Goiás State , Central Brazil

A new species of Microglanis is described from the upper rio Tocantins basin, Barro Alto, Goiás State, Brazil. This species is distinguished from the others by presenting a unique color pattern, consisting of round spots in the flank between the larger dark brown blotches. Moreover, it can be distinguished by the combination of the following features: caudal fin emarginate, the upper lobe slightly larger than the lower, lateral line relatively long, reaching vertical through posterior margin of the pelvic fin, and light stripe on supra-occipital region absent or very narrow and with irregular shape.


Introduction
Microglanis Eigenmann, 1912 is a group of catfishes easily identified by the small size (less than 8 cm SL), incomplete lateral line, body with large dark brown blotches, and premaxillary tooth plate laterally rounded (Schultz, 1944;Gomes, 1946;Mees, 1974).
The geographic distribution is very broad in South America, occurring in coastal rivers of the trans-Andean region of Peru and Ecuador, and in major watersheds of cis-Andean region (Shibatta, 2003).Among these, the Araguaia-Tocantins basin was only recently recognized as area of distribution of genus, with the description of three new species (Ruiz & Shibatta, 2010;Ruiz & Shibatta, 2011).Particularly to the rio Tocantins basin, only M. robustus Ruiz & Shibatta, 2010 was described to date, but with known distribution restricted to the region of Tucuruí hydroelectric power plant, in Jatobal, Pará State.
Recently, analyzing the collection of Microglanis of Instituto Nacional de Pesquisas da Amazônia (INPA), a new species was discovered from the upper rio Tocantins basin, rio dos Patos, Barro Alto.With the description of this new species, the number of known species of Microglanis (Jarduli & Shibatta, 2013) is increasing to 22, highlighting the Araguaia-Tocantins basin as one of the richest in Microglanis species.

Material and Methods
Morphometric variables of four specimens were taken point-to-point with digital caliper with accuracy of 0.01 mm, under a stereomicroscope.Both counts and measurements were taken on the left side of specimens whenever possible.Measurements were taken following Mori & Shibatta (2006), with addition of head depth (measured at vertical through posterior margin of eye), and body depth at dorsal fin origin, totaling 22 morphometric variables.All measurements were presented as percents of standard length (SL), and the subunits of head were also presented as percents of head length (HL).Meristic data included counts of gill-rakers, serrations of pectoral-fin spine, lateral line pores, and dorsal, pectoral, pelvic, anal and caudal-fin rays.Roman numerals indicate unbranched rays and Arabic numerals represent branched rays.In the diagnosis and description of species, the frequency of each meristic data is presented in parenthesis and the counts of the holotype are followed by asterisks.Only the holotype was x-rayed to count ribs and vertebrae.Two additional specimens of the new species were collected with sieves, euthanized by hyper exposure of anesthetic Eugenol (c.3000 mg/L; Lucena et al., 2013), fixed in 10% formalin solution and preserved in 70% ethanol.Specimens of M. robustus, other species of rio Tocantins basin, were used to perform the sheared Principal Components Analysis (McLeod, 1990).For this analysis, 19 variables were selected from original morphometric list (excluding pelvic fin length, posterior cleithral process length, and caudal peduncle length, due to limitations on number of morphometric variables accepted by the program).Physical (temperature) and chemical (dissolved oxygen, pH, and conductivity) variables were taken with multiparameter equipment, depth of water and river width were taken with measuring tape, and the velocity of water was calculated as the time (in seconds) covered by an fluctuant object in a distance of five meters. Institutional
Description.Morphometric data are presented in Table 1.Body depressed from snout to dorsal-fin origin; posteriorly compressed.Profile slightly oblique upward from snout tip to posterior nostril, slightly convex from posterior nostril to nape, and convex from nape to dorsal-fin origin.Profile from dorsal-fin origin to end of adipose-fin base almost straight (not considering adipose fin), oblique downward.Dorsal profile straighter on small specimens (Fig. 2).Ventral profile from tip of lower jaw to end of anal-fin base slightly convex, almost straight.More convex in young specimens (Fig. 2).Head large, wider than deep.Mouth terminal, slightly prognathous.Opercular membrane large, well developed.Eye relatively small, lateral-superiorly positioned, covered by skin.
Color in alcohol.Dorsal region of head, from tip of snout to nape, dark brown, ventrally continuing in suborbital and opercular region to horizontal passing through angle of mouth; intermediate region with light blotch.Ventral region Habitat.The specimens from the ribeirão Pouso Alegre were collected at the mouth of a creek amid the adventitious roots   of riparian trees that stand out from the banks.Attempts were made to collect in the region above this point, where the bed was rocky, but no specimen was captured.The ribeirão Pouso Alegre presents riparian vegetation in good condition, bedrock, with sand, clay litter, logs and branches at the mouth (Fig. 5), dissolved oxygen 7.8 mg/L, pH 7.65, conductivity 85ì S/cm, water temperature 22.5° C, mean depth 6.5±0.93 cm, mean width 4.1±0.66m, mean speed water 0.12±0.02m/s.Other nine species of fish were collected in the same location and are listed in Claro-García & Shibatta (2013).
Etymology.The specific epithet maculatus means spotted, an adjective from the Latin macula, in reference to the dark brown spots on the trunk.

Multivariate morphometrics analysis.
The first principal component retained 76.5% of the variance of morphometric variables, and all eigenvalues showed positive signs, which allows to interpret it as the representative of size (larger specimens to the right of graph).The second component retained 7.8% of the variance and on this axis there was discrimination between species (Fig. 6).Microglanis maculatus differed from M. robustus in this analysis by higher values of anal-fin base length, interorbital width and eye diameter (positive highest values), and smaller values of pectoral fin spine length, dorsal fin spine length and adipose fin base length (negative highest values; Table 2).The discriminatory nature of some characters coincided with its proportions with SL or HL (Table 1).
Discussion.The color pattern of M. maculatus was the first character to draw attention to a new species, and this study evidenced its uniqueness among congeners.Coloration pattern in Microglanis is quite variable and complex, resulting in a large number of configurations among the species of the genus.Even so, it is possible to observe in the literature that the color pattern proved to be useful for species identification.For example, among the species of the Araguaia-Tocantins basin, M. robustus has a dark and thin stripe at the base of the caudal-fin rays, at middle of caudal fin and at middle of dorsal fin (Ruiz & Shibatta, 2010), and M. xylographicus has dark brown body with light streaks on the flanks (Ruiz & Shibatta, 2011).Microglanis oliveirai is the only species that does not have a unique distinctive mark (Ruiz & Shibatta, 2011), although this condition helps to distinguish it from the other species of the basin.The shape of hooks on the anterior margin of the pectoralfin spine have been used as well to distinguish Microglanis  species (e.g., in M. zonatus all hooks on anterior margin are retrorse; Eigenmann & Allen, 1942).This character however, should be used with caution in M. maculatus due to ontogenetic variation on the hook morphology.Small specimens of M. maculatus may present only retrorse hooks while large specimens have antrorse and retrorse hooks.The analysis of hook morphology on the anterior margin of the pectoral spine on large and small specimens of M. maculatus, evidenced that all hooks are retrorse until the ninth hook (counting from the base of spine), and beyond the ninth hook, antrorse hooks become more numerous.The single hooks, as present in M. maculatus, is a very common character in Microglanis, but forked hooks is not related to the ontogenetic development, and it seems to be characteristic of M. robustus.
Noteworthy is the restricted geographic distribution of M. maculatus.Some Microglanis species apparently has a wide geographic distribution (e.g., M. cottoides in coastal rivers of Southern and South Brazil; Menezes et al., 2007)
, which may indicate large dispersal ability of these species.However, despite the sampling efforts in different locations of the upper rio Tocantins basin, M. maculatus was found only in the rio dos Patos basin, in Barro Alto.The species was not found in another 20 sampling points on different streams of the rio dos Patos and rio Maranhão basins (Claro-García & Shibatta, 2013), and neither on the ichthyological survey conducted in the Serra da Mesa (Bartolette et al., 2012), slightly on North of the type locality.The small number of specimens collected and the apparent restricted distribution of M. maculatus in the rio dos Patos basin, indicate that this species is rare.

Table 2 .
Morphometric data loadings, eigenvalues and percentages relating to the first (PC1) and second (sheared PC2) eigenvectors of Principal Components obtained from the analysis of combined samples of Microglanis maculatus (n = 4) and M. robustus (n= 9).