Corumbataia britskii, Katiane M. Ferreira & Alexandre C. Ribeiro, 2007

Katiane M. Ferreira & Alexandre C. Ribeiro, 2007, Corumbataia britskii (Siluriformes: Loricariidae: Hypoptopomatinae) a new species from the upper Rio Parana basin, Mato Grosso do Sul, Central Brazil., Zootaxa 1386, pp. 59-68 : 60-66

Corumbataia britskii , new species

Fig. 1

Holotype. LIRP 5884, 26.0 mm SL, Brazil, State of Mato Grosso do Sul, Chapadão do Sul, Córrego Pedra Azul (19°12’15”S 52°43’55”W), Rio Sucuriú, upper Rio Paraná basin (Fig. 2), 10 October 2003, K.M. Ferreira, R.Campos-da-Paz & E. Sá.

Paratypes. LIRP 4937, 5, 13.3-27.0 mm SL (2, 19.7-24.4 mm SL, c&s), as the holotype. All from Brazil, Mato Grosso do Sul State, Chapadào do Sul, Rio Sucuriú, upper Rio Paraná basin: LIRP 5897 (2, 17.0-23.6 mm SL, c&s), Córrego Pedra Azul (19°12’15”S 52°43’55”W), 23 August 2006, A.C. Ribeiro, M. Carvalho & O. Froehlich; LIRP 5898, (8, 17.6-24.7 mm SL), Córrego Fazendinha (19º14’43”S 52º39’11.2”W), 25 August 2006, A.C. Ribeiro, M. Carvalho & O. Froehlich.

Diagnosis. Corumbataia britskii differs from congeners by having a more depressed head profile (vs. more rounded in C. cuestae and C. tocantinensis ) (Fig. 3), by having a more developed and conspicuous tuft of enlarged odontodes on the tip of the supraoccipital (vs. its reduced condition found in C. cuestae and C. tocantinensis ) (Fig. 3), and by heaving a partially enclosed arrector fossae (vs. an almost completely enclosed arrector fossae in C. cuestae and C. tocantinensis ) (Fig. 4).

Description. Morphometric and meristic data given in Tables 1 and 2, respectively. Dorsal profile of the body convex from snout tip to dorsal-fin origin; slightly concave at dorsal-fin base; straight from end of dorsal-fin base to caudal-fin origin. Ventral profile of the body straight from the snout tip to anus; straight at analfin base; straight from end of anal-fin base to caudal-fin origin. Greatest body depth at dorsal-fin origin; least body depth at caudal peduncle. Greatest body width at opercular or cleithral regions. Body progressively narrowing caudally from cleithrum. Head rounded anteriorly in dorsal view; eyes dorsolaterally positioned. Oral disk slightly elliptical, narrowing posteriorly. Anterior oral disk lobe covered by papilla of about same size. Posterior disk lobe covered by papilla which decrease in size posteriorly. Maxillary barbel atrophied. Compound pterotic-supracleithrum-posttemporal with small perforations along its median and inferior margins.

Body entirely covered by plates, except on rostrum, region overlying opening of swim bladder capsule, around anus, and in pectoral-, pelvic- and anal-fin insertions. Scapular bridge exposed and covered by odontodes. Abdomen in adult specimens covered with small plates which are absent in young specimens. Body plates completely covered by odontodes. Larger odontodes neighboring the supraoccipital bone. Lateral line interrupted by gaps in middle region and in caudal peduncle in a young c&s specimen, but not interrupted in larger specimens.

Dorsal-fin origin located posteriorly to vertical through pelvic-fin origin. Adpressed pectoral fin extending over the pelvic-fin origin. Tip of pelvic fin reaching anal-fin origin in males and shorter in females.

Color in alcohol. Dark brown coloration on dorsal and lateral regions of body; ventral region yellowish and belly slight grayish. Numerous dark brown chromatophores distributed over head, forming a diffuse stripe from snout tip below eyes to posterior region of head. Chromatophores concentrated on dorsal- and anal-fin bases. Dark brown stripe extending from end of dorsal- to caudal-fin origin. Large diffuse dark brown midlateral stripe from snout tip, crossing eyes, extending to caudal-fin base. Large ventral dark brown stripe from around urogenital papillae to caudal-fin origin. Abdomen mostly unpigmented. Three to four transverse darkbrown stripes on dorsal-fin. Unbranched rays of pectoral, pelvic and anal fins with several scattered, widespread chromatophores not arranged in stripes. Caudal-fin mostly dark-brown with two unpigmented round spots on caudal-fin lobes.

Ecological notes. The new species was sampled in deforested areas in moderate to fast current streams. Corumbataia britskii was sampled in association with aquatic macrophytes or in the submerged portion of marginal vegetation. In its gut contents were found filamentous blue-green algae, chlorophyts, diatoms and periderm.

Distribution. Known just from two streams, Córrego Pedra Azul (type locality) and Córrego Fazendinha (19°12’15”S 52°43’55”W and 19°14’43”S 52°39’11.2”W, respectively). Both streams are tributaries of the Rio Sucuriú, a right tributary of the upper Rio Paraná basin in the Mato Grosso do Sul State, Brazil.

Etymology. Named after Dr. Heraldo A. Britski, Museu de Zoologia da Universidade de São Paulo ( MZUSP), in recognition of his many contributions to our understanding of Hypoptopomatinae catfishes.

Discussion

The phylogenetic relationships of Corumbataia is presently somewhat obscure. Schaefer (1991, 1997, 1998) provided a phylogenetic analysis of the Hypoptopomatinae at the level of genera, recognizing it as a monophyletic unit and providing evidence for two natural subgroups within the subfamily, the tribes Otothyrini and Hypoptopomatini. Britski (1997), based on the set of characters presented by Schaefer (1991), included Corumbataia in the Otothyrini. This generic placement was not tested subsequently by Schaefer (1998), who did not include Corumbataia in his analysis. Recent papers (Ribeiro et al. 2002; Ribeiro et al. 2005) concerning the inclusion of new taxa within Schaefer’s phylogenetic framework have not provided substantial changes in hypoptopomatine topology, and are in agreement with Schaefer’s main conclusions. However, Gauger & Buckup (2005), in including in a phylogenetic analysis two new species of Parotocinclus , several undescribed cascudinhos, as well as Corumbataia , concluded that Schaefer’s Otothyrini is not monophyletic. These authors presented two alternative cladograms in their reanalysis of the Hypoptopomatine. In one of them, Corumbataia appears in a group that includes Microlepidogaster , Pseudotocinclus , Schizolecis , Pseudotothyris and Otothyris , all of which belonged to Schaefer’s original concept of Otothyrini, corroborating the previous generic placement of Corumbataia made by Britski (1997).

We confirm in C. britskii all of the characters presented by Schaefer (1998) supporting the Otothyrini, except his character 35 (presence of a rostral plate with posterior notch articulating with mesethmoid - Corumbataia presents a naked snout tip in which the rostral plate is absent), which are: presence of a deep metapterygoid channel (character 13, state 2), presence of a preopercle with a medially reflected ventral margin(character 18, statel), and presence of a ventrally expanded fourth infraorbital (character 37, statel).

According to Britski (1997), C. cuestae and C. tocantinensis should be differentiated only by counts of premaxillary and dentary teeth (23-28, 21-26 vs. 27-40, 26-39, respectively). However, Ferreira et al. (2006) also found citogenetic differences between C. cuestae and C. tocantinensis . Both species present biarmed chromosomes, but in C. cuestae the chromosomes are more metacentric while in C. tocantinensis they are more submetacentric. Furthermore, we observed that the two species can also be differentiated by color pattern, as the unbranched caudal-fin rays of C. britskii and C. tocantinensis lack the striped pattern present in C. cuestae (Fig. 5). Corumbataia tocantinensis and C. cuestae are more similar to each other in the morphology of the pectoral skeleton (Fig. 4). Both species share almost completely enclosed arrector fossae, which is partially opened in C. britskii . The lateral portions of the cleithra are wider in C. britskii than in the other two species.

Britski (1997) mentioned sexually dimorphic features for both C. cuestae and C. tocantinensis . Males differ from females by presenting a developed urogenital papillae posterior to the anus, a skin fold at the dorsal portion of the pelvic-fin spine, and a much longer pelvic-fin spine that extends over the first anal-fin ray. We confirmed all these characters in C. britskii and also observed that males of this species differ from females by having four white blotches on the caudal-fin, two at the dorsal lobe and two at the ventral lobe. Females, on the other hand, present only two white blotches, one on each lobe (Fig. 5A, B).