Trichomycterus pauciradiatus, Aline R. Alencar & Wilson J. E. M. Costa, 2006

Aline R. Alencar & Wilson J. E. M. Costa, 2006, Trichomycterus pauciradiatus, a new catfish species from the upper rio Paraná basin, southeastern Brazil (Siluriformes: Trichomycteridae)., Zootaxa 1269, pp. 43-49 : 44-48

Trichomycterus pauciradiatus , new species

(Fig. 1)

Holotype. UFRJ 5831 , 52.0 mm SL; Brazil: Estado de Minas Gerais: Municipio de Carrancas, corrego Debaixo da Serra, stream tributary of corrego Agua Limpa, rio Parana basin , 21°26’40”S 44°36’09”W; R. Campos da Paz, 27 March 2001.

Paratypes. MCP 38978 , 6 ex., 31.2-33.9 mm SL; UFRJ 5830 , 1 ex., 49.2 mm SL; UFRJ 5807 , 22 ex., 24.6-42.7 mm SL; UFRJ 5808 , 6 ex., 35.7-39.3 mm SL (c&s); all collected with holotype.

Diagnosis: Distinguished from all other species of the genus in having four pelvic-fin rays (vs. five). Similar to T. reinhardti (Eigenmann) by having a unique color pattern composed of a broad dark brown stripe on the flank, dorsally bordered by a bright yellow zone without dark marks. The new species differs from T. reinhardti by possessing a more slender body (body depth 12.6-15.1% SL vs.10.5-12.9% SL) and a shorter preorbital length (25.7-39.3% HL vs. 41.7-46.2% HL) (Tables 1 and 2).

Description: Morphometric data of holotype and paratypes are given in Table 1. Body elongated, subcylindrical on anterior portion, compressed on caudal peduncle. Dorsal profile slightly convex between snout and end of dorsal-fin base, straight to slightly convex on caudal peduncle. Ventral profile straight between lower jaw and end of anal-fin base, straight on caudal peduncle. Greatest body depth on vertical just in front of dorsal-fin origin. Skin papillae minute. Urogenital papilla conical, in vertical through anterior third of dorsal-fin. Dorsal-fin approximately triangular, origin on vertical through centrum of 20th or 21st vertebra. Anal fin triangular, origin on vertical through base of dorsal-fin ray 7-8 and through centrum of 24th or 25th vertebra. Pectoral-fin small, about triangular, lateral and posterior edges slightly convex. First pectoral-fin ray terminating in filament about 5-10% of pectoral-fin length. Pelvic-fin about half of anal fin, covering urogenital pore, tip not reaching anal fin, in vertical through anterior portion or middle of dorsal fin; pelvic-fin bases separated; pelvic-fin origin in vertical through centrum of 18th or 19th vertebra. Caudal fin truncate. Dorsal-fin rays 10-12; anal-fin rays 9; pectoral-fin rays 6; pelvic-fin rays 4; caudal fin principal rays 13, dorsal procurrent rays 14-16, ventral procurrent rays 11-13. Total vertebrae 36-38; pleural ribs 14-16. Upper hypural plates ankylosed; single lower hypural plate and parhypural completely fused.

Head depressed, longer than wide, about quadrate in dorsal view. Snout blunt. Mouth subterminal. Maxilla short, slightly longer or equal to premaxilla. Teeth incisor. Eye approximately at middle of head. Tip of nasal barbel reaching posterior margin of opercular patch of odontodes. Tip of maxillary barbel reaching posterior margin of interopercular patch of odontodes. Tip of rictal barbel reaching between posterior portion of head and pectoral-fin insertion. Eight branchiostegal rays. Interopercular patch of odontodes long, with 30-34 odontodes; opercular patch of odontodes wide, with 14-18 odontodes; odontodes conical, opercular odontodes about equal interopercular odontodes; opercular odontodes arranged vertically. Medial margin of autopalatine slightly concave, with median expansion; posterior process of autopalatine equal in size autopalatine without posterior process. Lacrimal about one fourth of supraorbital length.

Supraorbital canal with three pores; first pore in transverse line through anterior nostril, second in close proximity to posterior nostril, third pore symmetrical to pore and orbit. Infraorbital canal with four pores; first pore in transverse line through anterior nostril, second one in transverse line just posterior to posterior nostril, third and fourth pores posterior to orbit. Preopercular canal with one pore, in vertical through anterior margin of opercular patch of odontodes. Lateral line of body short, with three pores, posteriormost pore on vertical just posterior to pectoral-fin base.

Coloration: Side of body yellow with broad dark brown stripe along lateral midline, dorsally bordered by a bright yellow zone lacking dark chromatophores; longitudinal row of dark brown small spots sometimes coalescent; below lateral stripe some dark brown dots irregularly distributed along ventral the portion of flank. Venter light yellow. Head yellow with dark brown spots on dorsal surface; dark brown blotch between eyes sometimes prolonged to posterior portion. Small spots sometimes coalescent around eye, and short dark brown bar in front of opercle. Ventral surface of head yellow with few dark brown dots. Nasal barbel brown, maxillary and rictal barbels light yellow. Pectoral fin pale yellow. Dorsal, anal and pelvic fins pale yellow. Caudal fin light yellow with central portion light brown.

Distribution: Known only from the type locality, córrego Debaixo da Serra, tributary of córrego Água Limpa, upper rio Paraná basin, southeastern Brazil.

Etymology: From the Latin pauci (few) and radiatus (with rays), referring to the reduced number of pelvic-fin rays.

Discussion

Some authors have tentatively defined putative monophyletic assemblages within the genus Trichomycterus based on the possession of unique morphological features (e. g., Costa, 1992; Barbosa & Costa, 2003; Bockmann & Sazima, 2004). However, no phylogenetic studies encompassing all species of this genus are available, making it difficult to discuss phylogenetic relationships of most species, especially those not exhibiting features used in previous studies.

Color pattern has been considered by some authors to be unreliable to diagnose species of Trichomycterus . However, color pattern has been showed to be a powerful instrument not only to diagnose species but also to establish, in agreement with other characters, possible monophyletic groups among species of the genus (Barbosa & Costa, 2003). In this regard, Trichomycterus pauciradiatus is possibly more closely related to T. reinhardti , which is endemic to the upper rio São Francisco basin, than to other congeners due to both species sharing a derived color pattern not found among congeners. This color pattern consists of a broad dark brown stripe along the lateral midline, bordered above by a light yellow longitudinal zone lacking dark marks.