Trichomycterus brachykechenos

description

Description. Morphometric data for holotype and paratypes in Table 4. Body elongate, trunk roughly cylindrical and gradually compressed towards caudal fin. Dorsal profile of trunk convex along anterior half then straight to insertion of dorsal fin. Ventral profile of trunk straight. Dorsal and ventral profiles of caudal peduncle slightly concave to straight. Head depressed, trapezoidal to square in larger specimens from dorsal view, wider posteriorly. Dorsal profile straight and ventral profile straight to slightly convex. Snout rounded from dorsal view. Eyes readily visible, rounded and dorsally oriented, orbital rim not free, eyes covered with skin thin and transparent. Each eye located over posterior termination of shallow and small longitudinal crest beginning at posterior nostril and making eyes visible from lateral view. Nostrils of same size and smaller than diameter of eye. Anterior nostril surrounded by fleshy flap of integument posterolaterally continuous with nasal barbel. Posterior nostril surrounded anterolaterally by thin flap of integument. Gill opening not constricted but united with isthmus anteriorly forming a free fold. Mouth subterminal with corners posteriorly

Taxonomic review of the genus Trichomycterus Valenciennes (Siluriformes: Trichomycteridae) from the laguna dos Patos system, Southern Brazil

diagnosis

Diagnosis. Trichomycterus brachykechenos is distinguishable from all congeners except T. megantoni Fernández & Chuquihuamaní, 2007 by its elongate posterior cranial fontanel which is restricted to the parietosupraoccipital (Fig. 2 d vs. the posterior fontanel extending from the parieto-supraoccipital to the frontals or posterior fontanel separated in two openings not restricted to the parieto-supraoccipital). Trichomycterus brachykechenos is distinguished from T. megantoni by the modal possession of I + 5 pectoral-fin rays (one among 15 specimens with I + 6 vs. I + 7 - 8 pectoral-fin rays), first ray of the pectoral fin not prolonged as a filament (Fig. 15; vs. the first ray of the pectoral fin prolonged as a filament), absence of the interopercle thickened ventrally (vs. presence). Trichomycterus brachykechenos is further distinguishable from all its congeners except T. mboycy, T. naipi, and T. poikilos by the modal possession of I + 5 pectoral-fin rays (one among 15 specimens with I + 6; vs. I + 6 or more pectoralfin rays) and the first ray of the pectoral fin not prolonged as a filament (Fig. 15; vs. first ray of the pectoral fin prolonged as a filament). Trichomycterus brachyke

Taxonomic review of the genus Trichomycterus Valenciennes (Siluriformes: Trichomycteridae) from the laguna dos Patos system, Southern Brazil

discussion

Remarks. The cranial fontanel demonstrates several modifications in the Trichomycteridae. The basal subfamilies Copionodontinae and Trichogeninae possess a completely open anterior cranial fontanel extended as a long slit from the mesethmoid to the epiphyseal bar (de Pinna, 1992 a). Ituglanis has only the posterior cranial fontanel which is reduced to a small round opening restricted to the parieto-supraoccipital (Costa & Bockmann, 1993) or is even absent in I. macunaima Datovo & Landim, 2005; I. mambai Bichuette & Trajano, 2008; and some I. epikarsticus Bichuette & Trajano, 2004 (Datovo & Landim, 2005; Bichuette & Trajano, 2008, 2004, respectively). A completely closure of cranial fontanels also occurs in the subfamilies Glanapteryginae, Stegophilinae, and Vandelliinae (Baskin, 1973). Bockmann et al. (2004) identified the anterior cranial fontanel partially or completely closed as a derived feature that corroborates the monophyly of clade 2 (sensu de Pinna 1992 a, 1998). In the Trichomycterus species the cranial fontanel is normally divided in two openings separated by epiphyseal bar: the anterior fontanel which is a small rounded opening situated between frontals, and the posteri

Taxonomic review of the genus Trichomycterus Valenciennes (Siluriformes: Trichomycteridae) from the laguna dos Patos system, Southern Brazil

distribution

Distribution and ecological notes. Trichomycterus brachykechenos is apparently endemic to the rio do Sinos, in the laguna dos Patos system (Fig. 8). At the locality where most types (11 specimens) were collected, the rio do Sinos is narrow (ranging from 5 to 9 m a. s. l.) and shallow (depth less to 1 m) with fast current and rapids, a distinct slope, clear waters, a substrate consisting mainly of large rocks, and conserved riparian vegetation (Fig. 9 d). The type locality is located at elevation of approximately 109 m a. s. l. and the two other type lots were from 169 m and 266 m a. s. l. The stomach contents of one c & s specimen contained larvae of the Chironomidae (Diptera) and pupa of the Diptera.

Taxonomic review of the genus Trichomycterus Valenciennes (Siluriformes: Trichomycteridae) from the laguna dos Patos system, Southern Brazil