Microglanis pataxo, a new catfish from southern Bahia coastal rivers, northeastern Brazil (Siluriformes: Pseudopimelodidae)

A new pseudopimelodid catfish of the genus Microglanis, collected in small rivers at the lower and middle Peruípe, middle Jucuruçu and Cahy basins, in the southeastern coast of the Bahia state, is described. The new species has a comparatively high number of anal fin proximal radials, 12, shaped as thin tubes, the last one bearing a laminar extension; a pectoral fin spine with a bony point and with a smaller number of serrations on its posterior border; seven pleural ribs and a narrow head width. We provide information on the external morphology and also on some osteological features for the new species. A key to species is presented for the coastal drainages between Rio de Janeiro and Bahia states.


Introduction
The genus Microglanis comprises catfishes that never grow to a size larger than 80 mm (Shibatta, 2003a).Those catfishes have a flattened large head, spines and fin-rays, a complete lateral line, but with pores distinct only on anterior parts of the body and on the head (Mees, 1974).They are beautifully colored fishes, with a characteristic light band running across the nape and alternate light and dark blotches over the body.
The genus Microglanis was proposed by Eigenmann (1912) to include small pimelodid catfishes, rarely attaining more than 70 mm in standard length.Shibatta (1998) included Microglanis in the small family Pseudopimelodidae, containing catfishes with a wide mouth, small eyes without free orbital margin, and short barbels.The genus is considered monophyletic on the basis of putative autapomorphic features such as premaxillary bands of teeth with lateral margin rounded, mesocoracoid arch filamentous, and body size smaller than 80 mm (Shibatta, 2003a).Microglanis has the widest distribution within the family Pseudopimelodidae (Shibatta, 2003b), with fourteen known species ranging from the Guianas, Venezuela, western slope of the Andes in Ecuador and Peru, to the Rio de La Plata basin in Argentina.The northern species are M. iheringi Gomes, 1946, from the río Turmero, near Turmero, Aragua, Venezuela; M. pellopterygius Mees, 1978, from a tributary of the río Aguarico in Santa Cecília, Napo, Ecuador; M. poecilus Eigenmann, 1912, from Packeeo Falls, Guyana and French Guiana; M. secundus Mees, 1974, from the Marowijine, Saramacca, Coppename, rio Nickerie and rio Coratijin, in Suriname, rio Rupununi, in Guyana and also from rio Catatumbo, in Colombia; M. variegatus Eigenmann & Henn, 1914, from a pool in the Vince forest, Ecuador, and M. zonatus Eigenmann & Alen, 1942, from the rio Morona, upper rio Amazonas basin in Peru.One species, M. ater (Ahl, 1936), is supposedly recorded from freshwater river drainages at central Brazil, a record that is questionable according to Mees (1974), as the type locality is "Mittelbrasilien", with no exact localities known.Shibatta (2003b) states that this species occurs in South America, and the record from Brazil is questionable.The species recorded from southern South America are M. cibelae Malabarba & Mahler, 1998, from a tributary of the rio Maquiné, between Maquiné and Barra do Ouro, coastal drainages in northeastern Rio Grande do Sul and southern Santa Catarina, Brazil; M. cottoides (Boulenger, 1891), from the rio Camaquã, laguna dos Patos system, Rio Grande do Sul, and also from rio Uruguay basin, Brazil; M. eurystoma Malabarba & Mahler, 1998, from upper rio Uruguay, Santa Catarina, Brazil, and M. malabarbai Bertaco & Cardoso, 2005, from a tributary of rio Ijuí, middle rio Uruguay, Rio Grande do Sul, Brazil.One species was recently described for the upper rio Paraná basin, M. garavelloi Shibatta & Benine, 2005.Microglanis currently includes two species chiefly distributed in the coastal basins of eastern Brazil: Microglanis parahybae (Steindachner, 1880), from the rio Paraíba do Sul and Santa Cruz, Rio de Janeiro, Brazil and M. nigripinnis Bizerril & Peres-Neto, 1992, from the rio Macacu, Papucaia, Cachoeira do Macacu, Rio de Janeiro, Brazil.
The BIOBAHIA project (Diversity, endemism and biogeography of catfishes in less explored aquatic systems in the extreme southern Bahia) aims to provide an inventory of the freshwater fishes of the hydrographic systems opening to the Atlantic at southern Bahia region.Along with the cooperation of the Museu Nacional and the All Catfish Species Inventory Project, a recent ichthyological survey in northeastern Minas Gerais and southern Bahia rivers was undertaken, revealing a new species of Microglanis, which is described herein.

Material and Methods
Straight-line measurements were taken point to point under a stereomicroscope with a Mitutoyo digital caliper, and recorded in tenths of a millimeter.Measurements followed Malabarba & Mahler (1998) except the following: caudal peduncle length: from base of last anal fin ray to base of lower caudal fin unbranched ray; orbital diameter: greatest horizontal dimension of eye ball; snout length: from tip of snouth to anterior border of orbits; and interorbital width: between dorsal margins of eye.Standard length (SL) is expressed in mm and all other measurements are expressed as percents of standard length, except subunits of the head, which are expressed as percents of head length (HL).Vertebral counts included all rib-bearing centra but do not include any of the anterior, com-plex centrum elements without ribs, and included the compound caudal centrum (PU1+U1) as the last element.The direction of dorsal and pectoral-fin spine serrations are referred to as antrorse, for those pointing away from the base of spine, and retrorse, for those bent towards the base of the spine.Osteological terminology follows Arratia & Huaquin (1995) and Arratia (2003) and were verified in cleared and stained specimens (c&s), following the procedures of Taylor & Van Dyke (1985) or in radiographs (R) of specimens.Osteological information for M. cottoides, M. iheringi, M. parahybae, M. poecilus, M. variegatus, and M. zonatus were based on radiographs of specimens as listed under comparative material.External morphological data about Microglanis pellopterygius and also complementary information for M. iheringi, M. poecilus, M. variegatus, and M. zonatus were based on photographs (P).Information about Microglanis ater, M. eurystoma, M. malabarbai, M. nigripinnis, and M. secundus were based on literature (Mees, 1974;Bizerril & Peres Neto, 1992;Malabarba & Mahler, 1998;Bertaco & Cardoso, 2005), as no specimens of these species were available for examination.
The following acronyms are used to specify the repositories of material examined: AMNH, American Museum of Natural History, New York; ANSP, Academy of Natural Sciences of Philadelphia, Philadelphia; AUM, Auburn University Museum, Auburn; CAS, California Academy of Sciences, San Francisco; MNRJ, Museu Nacional, Rio de Janeiro; UF, University of Florida Museum of Natural History, Gainesville, and USNM, United States National Museum, Washington, D.C.

Microglanis pataxo, new species
Fig. 1 Holotype  Diagnosis.Microglanis pataxo can be identified by the color pattern with a dark blotch beneath adipose fin not extending to anal fin and by the high number of anal fin proximal radials, 12, shaped as rod-like thin tubes, the last one bearing a laminar extension.The new species can be also recognized by the following combination of characters: a pectoral fin spine with a bony point and bearing proportionally few serrations on posterior border of pectoral fin spine, eight to ten.Seven pleural ribs and a proportionally short head width (67.8-74.3% in HL).
Description.Morphometric and meristic data in Table 1.Body moderately short, head and anterior trunk depressed, becoming compressed posteriorly.Head large and dorsoventrally compressed, dorsal profile somewhat quadrangular.Dorsal profile of trunk from dorsal-fin base to caudal peduncle becoming gradually compressed laterally.Lateral profile of head from snout tip to opercular margin slightly convex; becoming straight until dorsal-fin origin.Head and anterior trunk rectangular in cross section, becoming elliptic posteriorly.Ventral profile of head and abdomen almost straight.Ventral profile of body gently curved posterior to anal fin.Caudal peduncle laterally compressed.Eyes very small, latero-superior and covered with skin.Mouth terminal, upper lip extended posterolaterally as fleshy rictal fold.Anterior nostril somewhat tubular, located on anterior border of snout, above lip; posterior nostril larger, rounded.Maxillary barbels short, reaching opercular membrane.Mental barbels four, arranged in arc along ventral surface of jaw.Inner mental barbels half length of outer mental barbels.Maxillary and mental barbels extending to pectoral fin base.Post-cleithral process slender and pointed.
Premaxilla transversely elongate, meeting its counterpart medially.Autopalatine tubular, oriented obliquely to longitudinal axis of body.Maxillary bone small, with large posterior border.Jaws of equal size.Premaxillary tooth patch not forming backwardly projecting angle.Premaxillary and dentary with four to five rows of minute conical teeth.
Dorsal-fin margin rounded, with one spine plus six branched rays.Dorsal-fin spine with anterior surface smooth and two to three small retrorse serrae on distal portion of posterior surface.Pectoral fin with one spine plus five branched rays.Pectoral-fin spine with serrae on both margins: the anterior margin serrae smaller than posterior ones.Anterior pectoral-fin margin with 13-16 serrae: those closer to base of spine retrorse, around middle of spine one or two perpendicular serrae and subsequent ones antrorse.Posterior surface of pectoral-fin spine has 8-10 retrorse serrae (Fig. 2).Pelvic-fin margin rounded, located below posterior edge of dorsal-fin.Pelvic with one unbranched plus five branched rays.Adipose-fin developed, with posterior margin free and angulose, not confluent with caudal-fin, and located above anal-fin origin.Anal-fin margin rounded, with two or three unbranched rays, plus one anteriormost reduced ray and seven to nine branched rays, not reaching caudal-fin base.Nine branched anal-fin rays rare, found only in one specimen.12 rod-like, thin anal-fin proximal radials, last one short and laminar (Fig. 3).Twelve distal radials completely cartilaginous.Caudal fin slightly forked, its upper lobe longer than lower, with 13-14 branched rays; principal rays 7+8; upper procurrent 15; lower procurrent nine.Total vertebrae 29.Seven pleural ribs becoming progressively small antero-posteriorlly.
Urohyal with expanded, narrowly paired lateral processes and short pointed posterior processes.Basibranchial 1 absent; basibranchial 2 plus 3 forming cartilaginous rod with anterior tip reaching dorsal surface of ceratohyal and posterior, osseous, tip nearly in contact with basibranchial 4. Basibrachials 2 plus 3 rod bordered laterally by cartilaginous head of hypobranchials 2 and 3. Basibranchial 4 bordered anteriorly by cartilaginous hypobranchials 3, laterally by cartilaginous head of ceratobranchials 4 and posteriorly by cartilaginous head of ceratobranchials 5. Hypobranchials 1 and 2 osseous, elongate, trapezoid, contoured with cartilage along its lateral and posterior borders.Hypobranchial 3 completely cartilaginous and approximately trapezoidal.Hypobranchial 4 absent.Five ceratobranchials present, mostly ossified, with cartilage on their extremities.First ceratobranchial giving support to single row of four finely-shaped elongated rakers.Second ceratobranchial also with single row of rakers.Third, fourth and fifth ceratobranchials with two rows of short rakers.Fifth ceratobranchial expanded posteromedially to support lower pharyngeal toothplate dorsally, with finely-shaped conical teeth arranged in four or five rows.Five epibranchials, first four largely ossified; except for its cartilaginous extremities.Epibranchials 1 and 2 rod-like, with short rakers arranged in one row.Epibranchial 3 with elongate posterior uncinate process.Epibranchial 4 broad, somewhat convex posteriorlly.Epibranchial 5 completely cartilaginous, placed between posterior cartilaginous tips of epibranchial 4 and ceratobranchial 4. Pharyngobranchial 1 absent.Pharyngobranchial 2 short, completely cartilaginous, placed between anterior cartilaginous tips of epibranchials 1 and 2 and subsequent pharyngobranchial.Pharyngobranchial 3 elongate, ossified, with well developed posterior border.Pharyngobranchial 4 ossified, giving support to upper pharyngeal tooth plate, with robust conical teeth arranged in four to five rows (Fig. 7).Color in alcohol.Head almost completely dark dorsally, with lighter areas below eyes and around cephalic lateral line pores.Conspicuous, transverse, light band just behind head, crossing pectoral-fin base, as typically for Microglanis species.First dark blotch shaped as large "x", around dorsal-fin base in dorsal view; and second one between dorsal and adipose fins.Adipose fin with characteristic dark band on its anterior or middle portion.Ventral region of head with dark melanophores, concentrated around mental barbels, and becoming sparse towards belly.Dorsal-fin base and spine dark, its distal portion crossed by large dark bar.Caudal peduncle with dark patch of coloration beginning in its central portion becoming larger towards its margins, triangle shaped, and ending in transverse dark bar onto caudal-fin base.Caudal fin with scattered dark melanophores and narrow dark bar along contour of each lobe, near its tip.
Live coloration.Ground color light brown with irregular dark areas on head, dorsal fin and between dorsal and adipose   fins.Caudal-fin base with conspicuous dark bar.Ventral surface of body lighter, with melanophores distributed on belly.Most fins hyaline with scattered melanophores over fin rays and membranes; dorsal fin with an irregular dark stripe along its longitudinal axis; adipose fin light brown with small patch of dark pigmentation near to its dorsal margin (Fig. 8).
Distribution.Microglanis pataxo is the first record of the genus in northeastern Brazilian rivers.The new species was found in coastal drainages of southeastern Bahia, in the drainages of rio Peruípe, rio Jucuruçu, and rio Cahy (Fig. 9).
Etymology.The specific name honors the Pataxó native indigenous people, who live in the neighbourhoods of the distribution area of the new Microglanis species.
Ecological notes.The river systems in southern Bahia cross a plain to undulate relief with sediments from Tertiary to Quaternary, responsible for the formation of "tabuleiros", the regional name in reference to the vast open plain left on landscape.Geologically those coastal "tabuleiros" belongs to the "Formação Barreiras", dated from the Pliocene, extending from the coast up to 110 km inland from Ilhéus, Bahia, to the mouth of rio Doce, in Espírito Santo (SRH, 1996).The whole study area was originally covered by the Atlantic Forest, but presently the vegetation around river drainages show different degrees of environmental conservation (MMA, 2000).At the rio Peruípe the vegetation was changed to eucalyptus tree groves, reminiscent of riparian vegetation only on river banks.The upper portion of rio Jucuruçu, called rio do Prado, is one of the heaviest impacted river system, being much deforested and occupied with pastures.The rio Palmares, a tributary of the rio Cahy, passes somewhat closer to the Pataxó indigenous village of Águas Belas, and the catfishes were captured downstream from the Palmares village.The small rio Cahy basin still has patches of original and secondary vegetation and riparian covering along the upper portions of its streams being partially protected in an environmental preservation area, the Parque Nacional do Descobrimento.The new Microglanis species was collected in the middle course of shallow waters, at a depth of 1 to 1.5 m.None of them were captured in the upper portions.Those catfishes were found in moderate flowing sections of the rivers, with sandy or gravel bottom.The environments were moderately vegetated and the water clear or brown (Fig. 10).In the stomach of two examined females (MNRJ 28398, 33.8 mm SL;MNRJ 28401, 23.9 mm SL), it was possible to identify small aquatic insect larvae and pupae.The 33.8 mm individual was a mature female, with large eggs in its gonads.

Discussion
The new catfish is recognized as Microglanis because it has the premaxillary bands of teeth with lateral margin rounded, a mesocoracoid arch filamentous, and body size smaller than 80 mm, characters diagnostic for the genus as stated by Shibatta (2003a).
The distinctive characters of the new species in relation to all Microglanis species is given in the diagnosis section.The recognition of M. pataxo from its geographically closest relatives deserves some comments.There are two Microglanis species recorded from coastal drainage between Rio de Janeiro and Bahia states: M. nigripinnis and M. parahybae.Microglanis nigripinnis is the most robust Microglanis species in the area.The color pattern promptly differentiates this species, as it is mostly black colored, with almost dark fins (Fig. 11a) (Bizerril & Perez-Neto, 1992).Besides coloration, it is quite distinct by its broad head almost as long as large (head width 96.2-100.0% in HL); deeper body depth (19.0-22.9%SL), nine branched anal-fin rays and 14 branched caudal-fin rays.In comparison to M. nigripinnis, M. pataxo has a different body coloration with alternate patches of irregular dark and light blotches and fins mostly hyaline, except for the dorsal fin with dark bands (Fig. 11c).Microglanis pataxo has a slender head, longer than larger (head width 67.8-74.3% in HL), body depth short (13.0-17.5% SL), branched anal-fin rays mainly 7 or 8, rarely 9, and 13-14 branched caudal-fin rays.
Microglanis parahybae is recognized by a pale area between pelvic and anal fins; as well as dorsal and caudal fins with dark bands (Fig. 11b) (Steindachner, 1880;Miranda Ribeiro, 1911;Caramaschi, 1991).Microglanis parahybae is herein recognized as having a highly variable color pattern, with some specimens darker resembling M. nigripinnis, and others with light and dark blotches such as in M. pataxo.The distinction between M. pataxo and M. parahybae is based on a comparatively wider head ; pectoral-fin spine with proportionally larger serrations on posterior margin and few in number, eight to ten (vs.small serrations and numerically more, 14-22, in M. parahybae); and pleural ribs 7 (vs.6 in M. parahybae).In comparison to both species in the area, M. pataxo is distinct regarding the short head width (67.8-74.3% in HL vs. 78.4-85.3% in M. parahybae as stated above and 96.2-100.0% in M. nigripinnis), and regarding the low number of 8-10 retrorse serrae in the posterior border of pectoral fin spine (vs.14-22 retrorse serrae in M. parahybae and 12-15 in M. nigripinnis).
Microglanis pataxo is quite similar to M. parahybae regarding some osteological features, such as the cranium, suspensorium, hyoid arch, and branchial skeleton.Regarding arrangement and number of anal-fin pterygiophores, M. pataxo has slender proximal radials, while its morphologically closest relative, M. parahybae, has broader ones.In M. parahybae there are laminar processes on the anterior proximal radials and uncinate process on the posterior ones, a condition found to be present in all the cleared and stained specimens examined, while in M. pataxo the radials are simple tubes (compare Figs. 3a and 3b).Anal-fin proximal radials bearing laminar projections were also recognized in radiographs of M. cottoides and M. poecilus, differing from the slender, rodlike, anal-fin proximal radials in M. pataxo.Osteological information in literature regarding the Microglanis species is available for M. cottoides and M. eurystoma in Guazzelli (1997), who observed a short supraoccipital process reaching the predorsal plate; a narrow anterior fontanel and a posterior fontanel opening as a pore.Those characters are in conformity of what was observed for the M. pataxo cranium.

Fig. 9
Fig. 9. a. Drainage map of eastern Brazil between rio São Francisco and rio Paraíba do Sul illustrating the distribution of the Microglanis species in the area.Dotted line indicates the study area.Symbols may represent more than one locality.b.Detail of collecting localities of Microglanis pataxo in the study area, between the rio Mucuri and rio Jequitinhonha.