PR OO FS A new species of Microglanis ( Siluriformes : Pseudopimelodidae ) from the rio Uruguay drainage , Brazil

A new pseudopimelodid catfish, Microglanis malabarbai, is described from the rio Ijuí drainage, tributary of the middle rio Uruguay, Rio Grande do Sul, Brazil. The new species is distinguished from all other Microglanis species by the caudal fin color pattern, almost completely black, with a narrow vertical white band across central portions of the caudal-fin rays. Furthermore, it is distinguished from M. cottoides and M. eurystoma, both from rio Uruguay drainage, by head length, maxillary barbel length, internareal distance, and number of lateral-line pores, and from M. cibelae from the coastal drainages of northern Rio Grande do Sul and southern Santa Catarina states, by head length, maxillary barbel length, and body width. A key is presented for the species of Microglanis occurring in southern Brazil.


Introduction
Microglanis is a genus of Neotropical pseudopimelodid catfishes comprising 12 valid species and distributed throughout most of tropical South America on both sides of the Andes (Shibatta, 2003a).The genus is known from Pacific coast drainage in Ecuador, Lake Maracaibo basin (rio Catatumbo), Orinoco basin, coastal drainages of the Guianas, Amazon basin, Río de la Plata basin, and coastal drainages of southern Brazil from the states of Rio de Janeiro to Rio Grande do Sul (Mees, 1974;Le Bail et al., 2000;Shibatta, 2003a).
Recently, Malabarba & Mahler (1998) reviewed the diversity of Microglanis in the rio Uruguay and coastal drainages of southern Brazil, recognizing three species.Microglanis cottoides (Boulenger, 1891) was considered valid, redescribed, and recorded from the rio Uruguay and rio Jacuí drainages, and two new species were described: M. eurystoma Malabarba & Mahler, 1998, from the upper rio Uruguay drainage, and M. cibelae Malabarba & Mahler, 1998, from the coastal drainages of northern Rio Grande do Sul and southern Santa Catarina states.
During inventory field studies conducted by the authors and related to the construction of two hydroelectric dams in the rio Ijuí, an additional undescribed species of Microglanis was discovered in this tributary of the middle rio Uruguay (Fig. 1), Brazil, which is described herein.

Methods and materials
Measurements were taken as described in Malabarba & Mahler (1998), including the following additional measurements: caudal peduncle length (measured from the base of the last anal-fin ray to the posterior margin of the hypural fan), dorsal-fin base, adipose-fin base, horizontal orbital diameter, maxillary barbel length, head depth (measured at a vertical immediately before pectoral fin spines), and

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internareal distance (measured between the bases of each nostril flap).Vertebrae, gill-rakers, branchiostegal rays, and procurrent caudal-fin ray counts were taken from cleared and stained specimens (c&s) prepared according to the method of Taylor & Van Dyke (1985).Vertebral counts include the caudal centrum, but not the fused elements of the Weberian apparatus.
Measurements were taken point to point with an electronic caliper on the left side of specimens when possible.Measurements are expressed as percents of standard length (SL) except subunits of the head, which are recorded as percents of head length (HL).Morphometric distances were explored using Principal Components Analysis (PCA) on the covariance matrix of log-transformed measurements to assess morphometric variation between species.PCA analyses were performed using the software PAST (Ryan et al., 1995).Factor scores were plotted in the SigmaPlot software (Brannan et al., 2000).Specimens examined belong to the following institutions: MCP, Museu The available samples of M. malabarbai were compared to both geographically isolated populations of M. cottoides from the rio Uruguay and laguna dos Patos drainages, and to type specimens of M. eurystoma and M. cibelae.

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Color in alcohol.Body alternately black and brownish yellow on sides and dorsum; light yellow ventrally.Head black in dorsal view, with transverse white bar connecting opercular openings, small white spot near each posterior nare, two white spots on cheek posteriorly and laterally to eye.Three wide vertical bars on sides of body; widest bar beneath dorsal fin, interrupted internally by light blotch and finishing laterally at lateral line; second bar continuous from base of adipose fin to that of anal-fin; third bar across caudal peduncle with small white spot near dorsal and ventral caudal peduncle profiles.
Pectoral and pelvic fins with series of small spots scattered on fin rays.Dorsal fin darkly pigmented, with white wedgeshaped blotch covering part of proximal half of three to four posterior rays; tip of all rays white.Adipose fin crossed in mid-length by black band continuous with second bar on body side.Anal fin crossed by dark black stripe near base, followed by white stripe, spotty black stripe, and white stripe near tip of rays.Caudal fin almost completely black, and some specimens with narrow vertical white band across central portions of caudal-fin rays.Tip of caudal-fin rays white (Fig. 2).
Distribution.Microglanis malabarbai is known only from the rio Ijuí, a tributary of the middle rio Uruguay, Rio Grande do Sul, Brazil (Fig. 1).

Discussion
The genus Microglanis was described by Eigenmann (1912: 155) to include small pimelodids with the head as wide as long, the skull covered by skin only; the occipital crest small; frontal fontanel not extending much if any behind the eye, and a minute occipital fontanel sometimes present; eye without a free orbital margin; dorsal and pectoral spines welldeveloped; and premaxillary patches of teeth without backward projecting angles.Furthermore, others authors (Schultz, 1944: 197-198;Gomes, 1946: 7-8;Mees, 1974: 221;1978: 259;Shibatta, 1998: 111) have evaluated the usefulness of the characters used to distinguish Microglanis from Pseudopimelodus.These genera differ in body size (Pseudopimelodus larger), posterior lateral line poorly developed in Microglanis, and especially in the shape of the premaxillary band of teeth (Mees, 1978).Recently, Shibatta (2003b: 396) presented three possible synapomorphies for Microglanis: (1) premaxillary bands of teeth with lateral margin rounded, (2) mesocoracoid arch filamentous, and (3) body size smaller than 8 cm, as well as two possible synapomorphies for Pseudopimelodus: (1) mesocoracoid arch depressed and triangular, and (2) pectoral-fin spine covered with thick skin.The new species here described has all characters proposed by Eigenmann (1912) as well as the possible derived features found by Shibatta (2003b) and is thus described in the genus Microglanis.
In M. malabarbai the caudal fin is almost completely black, with a narrow vertical white band, a character that is uncommon within the genus.All other Microglanis species have a wide vertical white band in medial caudal-fin portion or the caudal-fin is not pigmented.Malabarba & Mahler (1998) identified two populations of M. cibelae, one from the rio Tramandaí drainage (type locality of the species), and the other from the rio Canoas, tributary of rio Mampituba (northern coastal drainage) with caudal-fin color similar to M. malabarbai.Those fishes lack almost completely a vertical white band crossing the caudal-fin, and present an enlarged black area on pelvic and pectoral fins, versus scattered chromatophores observed on M. malabarbai.The new species also differs from M. cibelae with respect to the head length, body width, and maxillary barbel length (see diagnosis).

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Two other Microglanis species occur in the rio Uruguay drainage, M. eurystoma from the upper portions of this drainage, and M. cottoides (also occurs in the rio Jacuí drainage).These species do not appear to be syntopic with M. malabarbai.Comparisons of the two geographically isolated populations of M. cottoides (rio Uruguay and rio Jacuí drainages) showed no statistically significant differences (Figs.3-7, Table 1) and support their conspecificity as recognized Malabarba & Mahler (1998).The results of the principal components analysis (PCA) revealed a complete separation between M. malabarbai and the two populations of M. cottoides along the second principal component (Fig. 7).PC2 accounts for 6.0% of the total variance and corresponds primarily to differences in shape (vs.size), contains the main shape.Measurements loading strongly on PC2 are maxillary barbel length (0.57), internareal distance (-0.47), pectoral spine length (0.31), and mouth width (-0.28).
The new species described in this paper suggests that the rio Ijuí, tributary of middle rio Uruguay, has a substantial endemic component in its ichthyofauna.An undescribed cichlid fish species of the genus Gymnogeophagus (L.Malabarba and R. Reis, pers. commun.)and a probable new species of Hemipsilichthys (E.Pereira, pers.commun.)are also endemic to the rio Ijuí drainage, suggesting that the rio Ijuí represents a previously unrecognized area of fish endemism.These species occur in tributaries of the rio Ijuí above the natural waterfall located about 50 km upstream of its confluence with the rio Uruguay.This obstacle may be a Table 1.Morphometric data of the holotype (H) and paratypes of Microglanis malabarbai (n = 11, including the holotype), and M. cottoides from rio Uruguay (n = 12) and rio Jacuí (n = 33) drainages, Rio Grande do Sul, Brazil.

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natural barrier for the dispersal of these species.A hydroelectric dam will be constructed in the rio Ijuí above this natural waterfall, and the stream where the new species was collected will not be inundated.

Fig. 3 .Fig. 4 .
Fig. 3. Regression of head length as function of standard length in M. malabarbai and two populations of M. cottoides.Note that 95% confidence intervals do not overlap with those of compared species indicating statistically significant difference.

Fig. 5 .Fig. 6 .
Fig. 5. Regression of internareal distance as function of head length in M. malabarbai and two populations of M. cottoides.Note that 95% confidence intervals do not overlap with those of compared species indicating statistically significant difference.

Fig. 7 .
Fig. 7. Scatter plot of principal components analysis on covariance matrix of log-transformed measurements ofMicroglanis malabarbai (open circles) and two populations of M. cottoides from rio Uruguay (black circles) and rio Jacuí (black squares) drainages.