Trichomycterus giganteus, Sergio M. Q. Lima & Wilson J. E. M. Costa, 2004

Sergio M. Q. Lima & Wilson J. E. M. Costa, 2004, Trichomycterus giganteus (Siluriformes: Loricarioidea: Trichomycteridae): a new catfish from the Rio Guandu basin, southeastern Brazil., Zootaxa 761, pp. 1-6 : 2-5

Trichomycterus giganteus new species

(Fig. 1)

Holotype. UFRJ 5999 , 120.6 mm SL; Brazil: Estado do Rio de Janeiro: Municipio do Rio de Janeiro, Campo Grande, Rio Guandu-Mirim, Rio Guandu basin ; S. M. Q. Lima, R. Paiva & R. Salles, 20 February 2003 .

Paratypes. UFRJ 5730 , 10 ex., 116.2-138.7 mm SL; MCP 35028 , 4 ex., 112.6-137.8 mm SL; UFRJ 5732 , 2 ex. (c&s), 109.8-111.2 mm SL; all collected with holotype. UFRJ 5399 , 4 ex., 145.5-204.0 mm SL; UFRJ 5733 , 2 ex. (c&s), 140.4-147.1 mm SL; Brazil: Represa do Mendanha ; H. N. Cunha, 2 February 1986 .

Diagnosis: Distinguished from all other species of the genus by having a broad dark bluish gray stripe along lateral midline of body, restricted to inner layer of tegument, overlapped by superficial dark brown spots. Similar to T. nigricans Valenciennes and T. immaculatus (Eigenmann & Eigenmann) , and distinguished from the remaining species of the southeastern Brazil by having nine pectoral-fin rays (vs. eight or less), anal-fin origin at vertical posterior to dorsal-fin base (vs. through posterior portion of dorsal-fin base), and more odontodes (interopercular 59-70 vs. 30-52, opercular 23-30 vs. 10-20). Readily distinguished from T. nigricans and T. immaculatus by having longer nasal and maxillary barbels (nasal reaching pectoral fin base, vs. between orbit and opercular patch of odontodes; maxillary reaching anterior third of pectoral fin, vs. to interopercular patch of odontodes). Also distinguished from T. immaculatus by having a single median third supraorbital pore (vs. third supraorbital pore paired). This new taxon is unique among species of southeastern Brazil by having a dark gray opercular patch of odontodes (vs. light yellow). It is also the biggest species of this region, reaching about 200 mm SL (vs. 50-150 mm SL).

Description: Morphometric data for holotype and paratypes given in Table 1. Dorsalfin origin in vertical between centrum of 17th and 19th vertebrae. Anal-fin origin in vertical posterior to dorsal-fin base, and through centrum of 23rd or 24th vertebra. Pectoral fin nearly triangular, lateral and posterior edges slightly convex. First pectoral-fin ray terminating in long filament, about 50% pectoral-fin length. Pelvic fin length about 2/3 anal fin length, tip not reaching anal fin nor covering urogenital pore, in vertical through base of 2nd branched dorsal-fin ray; pelvic-fin bases separated by interspace. Caudal fin truncate. Dorsal-fin rays 12-13; anal-fin rays 10-11; pectoral-fin rays 9; pelvic-fin rays 5; caudalfin principal rays 13, dorsal procurrent rays 15, ventral procurrent rays 13-14. Total vertebrae36-37; pleural ribs 12-13. Upper hypural plates separated, dorsal plate slightly wider than ventral plate.

Head trapezoidal in dorsal view. Maxilla about as long as premaxilla. Teeth conical. Tip of nasal barbel reaching pectoral-fin base. Tip of maxillary barbel reaching anterior third of pectoral fin. Tip of rictal barbel reaching behind opercular patch of odontodes. Branchiostegal rays 7-8. Interopercular odontodes 59-60; opercular patch of odontodes wide, with 23-24 odontodes; odontodes conical, opercular odontodes wider than interopercular odontodes; opercular odontodes arranged vertically. Medial margin of autopalatine slightly concave; posterior process of autopalatine about half autopalatine length without posterior process. Lacrimal about one fourth supraorbital length; supraorbital rodlike. Metapterygoid small, without distinct processes. Anterodorsal surface of hyomandibula with weak concavity. Single median third supraorbital pore. Anterior section of infraorbital canal present.

Coloration: Side of body and head light yellowish brown, slightly greenish between dorsal surface of head and laterodorsal portion of flank anterior to dorsal-fin origin. Slightly purplish on dorsal portion of caudal peduncle; orange on ventral portion of flank between pelvic-fin base and anterior portion of caudal peduncle. Rounded brown blotches on dorsum, dorsal half of flank, and head, both in superficial and inner layer of integument, blotches of distinct layers sometimes overlapped. Broad dark bluish gray stripe along lateral midline, restricted to inner layer of tegument. Superficial brown dots below lateral midline; venter light brownish yellow. Opercular patch of odontodes dark gray, interopercular patch of odontodes pale yellow; barbels gray, dark brown on basal portion. Iris dark green. Dorsal fin orange with brown dots on basal portion, yellowish hyaline on distal portion. Caudal fin dark yellow with vertical rows of small dark brown spots, distal fourth hyaline. Pectoral, pelvic and anal fins pale orange with brown dots; pectoral-fin filament light gray.

Distribution: Upper Rio Guandu basin, Serra do Mendanha, southeastern Brazil.

Habitat notes: The type locality is a clear water stream with strong current. All specimens, however, were found in still water between 50 and 200 cm deep, hidden under rocks.

Etymology: From the Latin giganteus (gigantic) referring to the large size of the new species, the biggest among species from southeastern Brazil.

Discussion

Arratia (1998) provided a detailed redescription of the type species of the genus, Trichomycterus nigricans based on a single specimen deposited in the Muséum National d`Historie Naturelle, Paris. This redescription reveals some uncommon features among species from southeastern Brazil that are shared by T. nigricans , T. immaculatus , and T. giganteus , as noted in the present study: nine pectoral-fin rays and high number of odontodes in interopercular patch of odontodes (59-69). However, it is not clear at the present if these conditions are evidence of close relationships, since both may occur or not in other Trichomycterinae taxa from the Andean region, making polarization of character states ambiguous. Another interesting point concerning Trichomycterus giganteus is its very distinctive size, the biggest among species from southeastern Brazil. Surprisingly, this species is endemic to the Rio de Janeiro, one of the oldest and largest cities in South America, demonstrating the poor knowledge of trichomycterid diversity.