Two new species of Microglanis ( Siluriformes : Pseudopimelodidae ) from the upper-middle rio Araguaia basin , Central Brazil

Two new species of Microglanis are described from tributaries of upper-middle rio Araguaia, States of Mato Grosso and Goiás, Brazil. Microglanis oliveirai differs from its congeners by the short supraoccipital process not reaching the small anterior nuchal plate, and reduced number of gill rakers, lateral line pores, ribs, vertebrae, and caudal-fin rays. Microglanis xylographicus differs from its congeners by the presence of melanophores surrounding the neuromasts of the superficial lines, snout length 11.4-12.9% SL and body color pattern consisting of horizontal brown stripes similar to a wooden bark pattern. An identification key of Microglanis species from the Amazon basin is presented.


Introduction
Microglanis Eigenmann, 1912 is endemic to freshwaters of South America, where it has a wide geographic distribution that includes both sides of northern Andes, and also the region from Venezuela to Uruguay (Shibatta, 2003a).It is the most species-rich genus of the Pseudopimelodidae, comprising 19 species (Ruiz & Shibatta, 2010;Ottoni et al., 2010).Microglanis can be identified from the remaining pseudopimelodids by the following combination of characters: body size smaller than 80.0 mm SL, premaxillary tooth patch with a rounded lateral margin and no posterior projection, lateral line canal incomplete, a filamentous mesocoracoid arch, and no axillary pore (Mees, 1974;Shibatta, 1998;2003b).
In the last few years several species of Microglanis were described (Shibatta & Benine, 2005;Sarmento-Soares et al., 2006;Mori & Shibatta, 2006;Alcaraz et al., 2008;Ruiz & Shibatta, 2010;Ottoni et al., 2010), which indicates that the genus is both more species-rich and widespread than previously supposed.The only species of Microglanis previously recorded from the rio Tocantins/Araguaia basin is M. robustus Ruiz & Shibatta, 2010.In the present paper, two additional species are described from the upper-middle rio Araguaia basin in Brazil.

Material and Methods
Specimens of all species of Microglanis were examined, with the exception of M. ater Ahl, 1936, M. zonatus Eigenmann & Allen, 1942, and M. minutus Ottoni, Mattos & Barbosa, 2010, of which photographs and data from literature were analyzed.Morphometric characters of 234 specimens were taken pointto-point with digital caliper with accuracy of 0.1 mm, under a stereomicroscope.Counts and measurements were taken on the left side of specimens, with a few exceptions, when the structures were damaged or absent.Measurements were taken following Ruiz & Shibatta (2010), and expressed as percents of standard length (SL), except subunits of the head, which are recorded as percents of head length (HL).Meristic data included counts of dorsal, pectoral, pelvic, anal and caudal-fin rays, gill rakers, serrations of pectoral-fin spine, lateral line pores, and superficial neuromasts.Roman numerals indicate unbranched rays (uppercases as spines and lowercases as soft rays) and Arabic numerals represent branched rays.The location and number of pores of lateral line and superficial neuromasts were analyzed according to Ruiz & Shibatta (2010).In the diagnoses and descriptions of species, the frequency of each meristic data was presented in brackets and the counts of the holotypes are identified by asterisks.Counts of branchiostegal rays, vertebrae, ribs, pterygiophores, and procurrent caudal-fin rays were obtained from two cleared and stained (c&s) specimens of each species, prepared according to Dingerkus & Uhler (1977).Vertebral counts included only free centra (elements of the anterior complex centrum were not included), with the compound caudal centra (preural 1 + ural 1) counted as a single element.For analysis of food items, the entire digestive tract contents of two specimens of each species herein described were examined.Gas bladder nomenclature followed Birindelli & Shibatta (2011)

Microglanis oliveirai, new species
Fig. 1 Diagnosis.Maxillary barbel surpassing base of pectoral-fin spine.Mental barbels arranged in arc along ventral surface of jaw; outer pair surpassing base of pectoral-fin spines; inner pair shorter, slightly less than one-half length of outer mental barbels.Pectoral fin roughly triangular in dorsal and ventral views, rays I,5.Pectoral-fin spine long, strong, flat, recurved at midpoint, strongly serrated in both margins, covered by thin skin.Anterior margin of pectoral-fin spine with four to eight retrorse serrations proximally, followed by none to two Yshaped serrations, and two to seven antrorse serrations distally (total = 9-13[32]).Posterior margin with six to 10[32] retrorse serrations, larger than those of anterior margin.Tip of pectoral-fin spine strongly ossified (Fig. 2).Pectoral fin not reaching pelvic-fin base.Dorsal fin II,6 (spinelet present); rounded margin, slightly deeper than long.Dorsal-fin spine straight, smooth, shorter than soft rays and covered by skin.Dorsal fin not reaching adipose-fin base when adpressed.
Lateral line incomplete, not reaching the vertical through the first branched dorsal-fin ray; 3[1], 4[7], 5*[16], or 6[8] large pores, about half diameter of parieto-supraoccipital fontanel.Cephalic sensory canals with eight pores on mandibular canal; one on preopercle canal; four on infraorbital canal; one on antorbital branch of infraorbital canal; five on supraorbital canal; one on parietal branch of supraorbital canal; one on otic canal; and two on postotic canal.Parietal branch of supraorbital canal with one terminal pore.Cephalic neuromasts lines with three or four small neuromasts on nasal line, one on rostral line, four to six on mandibular line, two on anterior line, and two on supratemporal accessory line.Trunk neuromasts lines with two neuromasts on dorsal-trunk line, six to 12 on medium trunk line, five to eight on subdorsal-trunk line, and five to seven very small neuromasts on subventral-trunk line.
Color in alcohol.Ground color light brown.Ventral region of body and head pale with brown spots.Head dark brown, with lateral portions of head, margin of opercle, anterior and posterior nostrils, and pores of cephalic canals light colored.Wide, irregular light band passing through nape and anterior portion of trunk, immediately after opercular opening.Upper lip dark, lower lip light.Light barbels speckled with dark brown spots.Overall trunk color light brown, with faint vermiculated stripes.Three large dark brown blotches, appearing dorsally as saddle markings.First blotch similar to an inverted U, below dorsal fin, reaching horizontal line through axis of trunk.Second blotch more elongated, situated immediately below adipose fin, extending posteroventrally to reach the brown blotch at anal-fin base.In some specimens, this sub-adipose blotch is divided in two by a light band across the horizontal Table 1.Morphometric data of Microglanis oliveirai (n=32) and Microglanis xylographicus (n=18).SD = standard deviation.Limits include the lower and higher numbers in holotype and paratypes.axis of the body.Third blotch positioned at middle to posterior portions of caudal peduncle, roughly triangular-shaped, with one of vertices pointing anteriorly.Middle trunk-line neuromasts faintly surrounded by melanophores.Pectoral and pelvic fins hyaline, slightly speckled with brown pigmentation over rays.Medial to distal portion of pectoralfin spine with a large dark brown blotch.Dorsal fin mostly hyaline, a large dark blotch situated at anterior basal portion of fin, extending into dorsal-fin spine.A brown, narrow stripe running midway between dorsal-fin base and margin.
Adipose fin with one oval light blotch on anterior portion, followed by narrow brown stripe, and light area slightly speckled with melanophores.Anal fin mostly hyaline, speckled with melanophores, concentrated as a small, relatively diffuse anterior basal portion and, in large specimens, a weak, brown arched stripe, on middle portion of anal fin between the 3 rd and 6 th rays.Caudal fin hyaline, speckled with brown cromatophores, with one straight, vertical dark brown stripe on the base.In larger specimens a narrow stripe shaped approximately like the numeral three, located at the middle of the fin.
Etymology.Microglanis oliveirai is named in honor of Claudio de Oliveira, from the Universidade Estadual Paulista "Júlio de Mesquita Filho", campus Botucatu (SP), in recognition of his extensive contribution to the knowledge of Neotropical fish evolution.
Remarks.Specimens collected at the rio Cristalino basin have larger interorbital width and possess an overall darker coloration when compared with specimens of the rio das Mortes basin.Pectoral fin roughly triangular in dorsal and ventral view, I,5, when adpressed not reaching pelvic-fin base.Pectoral-fin spine strong, flattened, slightly arched, completely covered by thick skin, with large serrations on both sides.Anterior margin of pectoral-fin spine with seven to 11 retrorse serrations proximally, followed by none to two slightly forked or rarely Y-shaped serrations, and none to four small antrorse serrations (total = 9-14[18]).Posterior margin of pectoral-fin spine with five to eight [18] retrorse serrations, larger than those of anterior margin.Tip of pectoral-fin spine ossified and pointed (Fig. 6).Dorsal fin II,6 (spinelet present), inserted almost at anterior midbody, deeper than longer, margin slightly rounded, when adpressed usually reaching adipose-fin base.Dorsal-fin spine straight, smooth, covered by skin, about the same length of last branched ray.Pelvic fin i,5, its insertion situated at midbody, margin rounded, and when adpressed, not reaching anal-fin base.Adipose fin moderately long and deep, with posterior margin free and angular, not confluent with caudal fin, and located above anal-fin origin.Lateral line incomplete, but usually reaching or surpassing vertical line through posterior portion of dorsalfin base; 7[3], 8 [6], 9 [5], 10*[2], 11[1], or 12[1] small pores.Cephalic sensory canals with eight pores on mandibular canal, one on preopercle canal, four on infraorbital canal, one on antorbital branch of infraorbital canal, five on supraorbital canal, one on parietal branch of supraorbital canal, one on otic canal, and two on postotic canal.Pterotic branch deprived of pores.Cephalic neuromasts lines with four or five small neuromasts on nasal line, one on rostral line, five to seven on mandibular line, two on anterior line, and two on supratemporal accessory line.Trunk neuromasts lines with two neuromasts on dorsal-trunk line, six to 13 on medium trunk line, five to eight on subdorsal-trunk line, and four to eight small neuromasts on subventral-trunk line.
Color in alcohol.Body almost entirely brown; anterior region darker; lateral portions of trunk and caudal peduncle with light brown horizontal streaks, imparting a pattern similar to tree bark, more concentrated on dorsal and median regions of body.Dorsal region of body completely dark brown, ventral region slightly mottled with brown spots.Head dark brown, with one lateral black stripe that extends to a region anterior to nostrils, uniting eye to upper lip.Upper lip dark, lower lip light.Barbels (mainly maxillaries) slightly mottled with brown.Melanophores surrounding neuromasts of all superficial lines, forming small, conspicuous black dots distributed in three horizontal rows along lateral portion of body, two dots above opercular opening, four dots on posterior top of head, and four dots on predorsal region.Caudal peduncle with a weak brown blotch of irregular shape.Pectoral, pelvic, anal and caudal fins hyaline, with speckled brown pigmentation roughly arranged in rows along fin rays.Dorsal fin with two conspicuous horizontal dark brown stripes, the first basal and wide, the second a little above dorsal-fin middle half, absent in small specimens.Dorsal-fin spine dark brown, pectoral-fin spine light brown, with dark brown speckles.Anterior portion of adipose fin light, followed by a dark brown blotch, central and posterior portions light-colored, with small irregular light brown blotches.Anal fin mostly hyaline, with dark speckling and with small brown blotches on anterior margin, absent in small specimens.Caudal fin hyaline, speckled with light brown pigmentation forming weak, vertical light brown stripes over fin rays; a wide, conspicuous, straight vertical stripe at caudal-fin base, and a second, considerably less conspicuous vertical stripe, situated slightly after caudalfin middle half, roughly shaped like the numeral three, present only in large specimens.
Distribution.Microglanis xylographicus is known from tributaries of the rio das Mortes and small nearby direct tributaries of the rio Araguaia such as the córrego Jaraguá (Fig. 3B) and rio das Garças, in States of Mato Grosso and Goiás, Brazil (Fig. 4).
Etymology.The name xylographicus is derived from the Greek xylos referring to wood, and graphikos, of writing.It is a reference to the horizontally striated color pattern, like a tree bark.An adjective.
Remarks.Specimens from the type locality, the córrego Jaraguá, are larger than specimens collected at the rio Insula  , have more neuromasts on median-trunk line (11)(12)(13), smaller dorsal-fin spine length (11.8-13.1% vs. 12.9-16.2%SL), larger posterior cleithral process length (11.7-12.2% vs. 9.2-11.6%SL), smaller adipose-fin base length , and a darker brown color.The two populations are separated (about 90 km) by the Serra do Roncador and Serra Azul, indicating that those differences might be geographically related.In the absence of additional evidence, we consider that the two populations belong to a single species.

Discussion
The two species of Microglanis described herein are apparently endemic to the tributaries of the upper-middle rio Araguaia.They occur sympatrically in the rio Corrente (Fig. 3C), which is also the type locality of M. oliveirai.The rio Corrente runs across a wide expanse of Cerrado vegetation (Central Brazil Savanna).It has a maximum depth of about 2.5 m, and a width of 6 to 11 m.The bottom of the river consists mostly of mud, with sandy patches and some gravel, and abundant submerged leaf-litter.Physical and chemical properties of the water at the moment of collection were: water transparency=0.15m, pH=6.4,temperature=22.1ºC,and conductivity=1.132μS/cm.Specimens of M. oliveirai and M. xylographicus were collected together in small peripheric pools formed by a shallow branch of the rio Corrente, amidst roots of the marginal vegetation, tree branches, and submerged leaflitter.It is generally accepted that species with similar morphologies and ecologies can not coexist in the same portion of a habitat, according to Gause's competitive exclusion principle (Hardin, 1960).In the case of M. oliveirai and M. xylographicus, competition might be avoided by the partitioning of resources (sensu Ross, 1986).This is a subject that should be properly addressed in future studies, but in order to offer some initial insight into this question, the digestive tract of two specimens of M. oliveirai and two specimens of M. xylographicus were examined.The stomach contents of all four specimens included only autochthonous aquatic insects, a result expected for benthic catfishes.The analysis also revealed that the dissected specimens of M. oliveirai consumed 67% of larvae of Chironomidae and 33% of larvae of Trichoptera, while 100% of the stomach contents of M. xylographicus were composed of larvae of Chironomidae.
Small adult size is a feature that consistently distinguishes Microglanis from other genera of the Pseudopimelodidae.Among the six Amazonian species of Microglanis that have been described so far, the largest is M. pellopterygius, whose maximum recorded length is 54 mm SL.The species of Microglanis from the eastern South America, M. parahybae, M. pataxo Sarmento-Soares, Martins-Pinheiro, Aranda & Chamon, 2006, M. leptostriatus Mori & Shibatta, 2006, and M. minutus, are also small-sized, with a maximum recorded length of 44.7 mm SL in M. parahybae.The largest lengths recorded in species of Microglanis are those of M. cottoides, with 68 mm SL, from the rio Ribeira de Iguape (Oyakawa et al., 2006), and M. eurystoma, with 77.6 mm SL, from the rio Uruguay (Malabarba & Mahler, 1998), which also marks the southern limit of distribution of the genus.Following the trend observed in the previously known Amazonian species, the two species of Microglanis described herein are also extremely small-sized, with up to 27.8 mm SL in M. xylographicus.
Microglanis oliveirai shares several features with M. poecilus, the most widely distributed species in the genus, which occurs across several river systems in Guyana, French Guiana, Venezuela (rio Orinoco basin), Suriname, and Brazil (rio Amazon basin).The two species share (1) a low and elongated body, (2) a wide light transversal band crossing the nape, (3) a short lateral line canal, not surpassing the vertical line through the middle dorsal-fin base, (4) few pores in the lateral line, ( 5) rays of the pectoral and pelvic fins slightly brown pigmented, ( 6) the middle to distal portion of the pectoral-fin spine with a small oval brown blotch, (7) the anterior margin of the pectoralfin spine with well-developed serrations, one of them Y-shaped between the series of retrorse and antrorse serrations, (8) a small brown blotch similar to an inverted U below the dorsal fin, reaching the horizontal line through the axis of the trunk, (9) a brown blotch below the adipose fin, reaching the anal-fin base, usually with a notch on its middle portion, (10) a roughly triangular blotch on the caudal peduncle, with one of its vertices directed anteriorly, and (11) the upper lobe of caudal fin larger than the lower lobe.However, M. oliveirai can be distinguished from M. poecilus by the relatively lower numbers of gill rakers, lateral line pores, vertebrae, and branched caudal-fin rays.
Microglanis xylographicus and M. robustus, from the lower rio Tocantins basin, are similar in a series of features, such as (1) the absence of a light stripe crossing the nape, (2) melanophores surrounding the neuromasts, together forming a series of small black dots aligned on the head, nape, predorsal area, and trunk, (3) rays of pectoral, pelvic, anal and caudal fins with speckled brown pigmentation roughly arranged in rows, and (4) upper lobe of caudal fin slightly larger than lower lobe.Microglanis xylographicus can be easily distinguished from M. robustus by the possession of a dark brown body color with narrow light stripes, together imparting a tree bark-like color pattern, the absence of a light area in the center of the dark brown blotch below the dorsal fin, and a longer snout length.