Trichomycterus perkos

description

Description. Morphometric data for type series given in Table 1. Refer to Figs. 1 – 2 for general external aspects. Body elongate. Dorsal and ventral profiles of trunk ranging from straight to slightly convex; dorsal and ventral profiles of caudal peduncle from straight to slightly concave. Cross section of trunk nearly oval, becoming gradually more compressed posterior to pectoral girdle. Head wide, depressed, trapezoidal in dorsal view. Larger specimens usually with region lateral to eyes swollen by hypertrophied adductor mandibulae A 2 A 3 muscles. Dorsal profile of head straight; ventral profile ranging from straight to convex. Eyes on dorsolateral region of head, progressively migrating towards more dorsal position with specimen growth. Orbital rim not free. Thin and translucent skin covering eye, not adhered to eyeball surface and forming anteroposteriorly elongated ocular capsule. Anterior nostril surrounded by tubular flap continuous with nasal barbel base; posterior nostril opening slightly smaller than anterior one and with crescent thin flap on anterior border. Mouth subterminal and slightly curved. Lower lip with lateral fleshy lobes posteromedial to rictal-barbel base.

A new species of the catfish genus Trichomycterus from the La Plata River basin, southern Brazil, with comments on its putative phylogenetic position (Siluriformes: Trichomycteridae)

diagnosis

Diagnosis. Large-sized specimens (more than 65.8 mm SL), presumably adults, of Trichomycterus perkos are distinguished from all their congeners in having a distinctive coloration with melanophores arranged in two distinct skin layers, forming (1) a freckled pattern, with minute light brown spots scattered on the superficial tegumentar layer of the dorsum and caudal peduncle, and (2) a striped pattern, with three – sagittal, midlateral, and ventrolateral – wide, irregularly bordered, and sometimes interrupted dark brown stripes running along an inner skin layer of the trunk and caudal peduncle (Fig. 1; vs. melanophores in only one skin layer in most other Trichomycterus or melanophores occurring in two layers, but with the inner layer forming blotches in T. brasiliensis Lütken, T. castroi de Pinna, T. crassicaudatus Wosiacki and de Pinna, T. diabolus Bockmann, Casatti, and de Pinna, T. igobi Wosiacki and de Pinna, T. maracaya Bockmann and Sazima, T. mimonha Costa, T. stawiarski (P. Miranda Ribeiro), and T. tropeiro Ferrer and Malabarba, or forming solely a midlateral stripe in T. giganteus Lima and Costa; pers. obs.; Bockmann et al., 2004; Bockmann & Sazima, 2004; de Pinna, 1992 b;

A new species of the catfish genus Trichomycterus from the La Plata River basin, southern Brazil, with comments on its putative phylogenetic position (Siluriformes: Trichomycteridae)

distribution

Distribution. A single paratype (MZUSP 82372) is from the Tibaji River basin, a tributary of the Paranapanema River (Fig. 3; see Discussion below). All remaining type series is from two sub-basins of the Uruguai River system, the Ijuí and Passo Fundo drainages (Fig. 3). The Paranapanema is an affluent of the Paraná River, which joins the Uruguai to form the La Plata River / Estuary. Habitat notes. Ecological data from all localities is unavailable. Most types were collected in clear water streams with 1 to 3 m wide, with bottoms composed of stone, gravel, and sand (Fig. 4). Streamlets were usually surrounded by modified riparian vegetation.

A new species of the catfish genus Trichomycterus from the La Plata River basin, southern Brazil, with comments on its putative phylogenetic position (Siluriformes: Trichomycteridae)

etymology

Etymology. From the Greek perkos (περκς), meaning “ spotted or streaked with black marks (Valpy, 1826: 227), in allusion to the color pattern of the new species formed by either dark stripes (small-sized specimens) or dark stripes combined with small spots (larger individuals). An adjective.

A new species of the catfish genus Trichomycterus from the La Plata River basin, southern Brazil, with comments on its putative phylogenetic position (Siluriformes: Trichomycteridae)