Trichomycterus poikilos

description

Description. Morphometric data for holotype and paratypes in Table 3. 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 to slightly convex. Dorsal and ventral profile of caudal peduncle straight. Head depressed, trapezoidal from dorsal view, wider posteriorly. Dorsal profile straight and ventral profile straight to slightly convex. Snout rounded from dorsal view. Eyes readily visible, anteroposteriorly elliptical and dorsally oriented; orbital rim not free, eyes covered with skin thin and transparent. Each eye located over posterior termination of shallow 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 openings not constricted but united with isthmus anteriorly forming a free fold. Mouth subterminal with corners posteriorly oriented. Low

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

diagnosis

Diagnosis. Trichomycterus poikilos is distinguishable from all congeners except T. brachykechenos; T. mboycy Wosiacki & Garavello, 2004; and T. naipi Wosiacki & Garavello, 2004 by the modal possession of I + 5 pectoral-fin rays (one among 82 specimens with I + 6; vs. I + 6 or more pectoral-fin rays) and the first ray of the pectoral fin not prolonged as a filament (Figs. 13 - 14; vs. the first ray of the pectoral fin prolonged as a filament). Trichomycterus poikilos is distinguished from T. brachykechenos by having the posterior fontanel extending from the parieto-supraoccipital to the frontals (Fig. 2 c; vs. the posterior cranial fontanel restricted to the parietosupraoccipital), the origin of dorsal fin located at the vertical falling between the tip of the pelvic fin and the anterior insertion of the anal fin (Figs. 13 - 14; vs. the origin of dorsal fin located at the vertical through the last third of the pelvic fin), the maxillary barbel length (33.2 - 60.4 % vs. 68.2 - 87.7 % HL), and the number of odontodes of the opercular patch (13 - 17 vs. 8 - 11). Trichomycterus poikilos is distinguished from T. mboycy by the pectoral-fin length (7.7 - 9.1 % vs. 9.9 - 13.8 % SL) and skin

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

discussion

Remarks. Trichomycterus poikilos demonstrates intraspecific ontogenetic color pattern variation. Although Bockmann & Sazima (2004) considered the body pigmentation pattern highly conserved in known species of Trichomycterus, a intraspecific variation in coloration is present in T. caipora Lima, Lazzarotto & Costa, 2008 (Lima et al., 2008), in T. iheringi (Eigenmann, 1917) associated to body size and microhabitat preference (da Silva et al., 2010), and in T. santanderensis Castellanos-Morales, 2007. The ontogenetic variation in T. poikilos is clear in lot UFRGS 14992 (six specimens with 40.5 - 92.5 mm SL), in which the smallest specimens have one obvious midlateral stripe on the body that gradually become indistinguishable in the largest specimens (Fig. 14). This ontogenetic variation is not observed in all samples. In other lots all specimens have a mottled pattern (UFRGS 14500, 11 specimens with 32.0 - 74.5 mm SL) regardless of body size. Besides coloration no additional differences were found between these populations that allow us to separate them and ontogenetic variation in the color pattern seems to appear only in some populations. The color pattern of some specimens of T. po

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

distribution

Distribution and ecological notes. Trichomycterus poikilos is distributed in the rio Jacuí, rio Pardo and rio Taquari-Antas basins, in the laguna dos Patos system (Fig. 8). The species is widely distributed in the upper portion of rio Jacuí basin, occurring at elevations of 124 to 700 m a. s. l. One lot is from the headwaters of rio Pardo basin, at 625 m a. s. l. In the Taquari-Antas basin the species occurs in the upper portions of the Carreiro, Guaporé, and Forqueta rivers, between 417 and 688 m a. s. l. The type locality is a rapid flow river with clear water, a rocky bottom and submerged vegetation (Fig. 9 c), located at approximately 405 m a. s. l. At this site the specimens were associated with submerged vegetation and collected with Ancistrus brevipinnis (Regan, 1904), Eurycheilichthys limulus Reis & Schaefer, 1998, and Rineloricaria cadeae (Hensel, 1868). The stomach of six c & s specimens contained aquatic larvae of Diptera (Simuliidae) and Lepidoptera; and nymphs of the Ephemeroptera and Plecoptera.

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