Trichomycterus diatropoporos

description

Description. Morphometric data for holotype and paratypes in Table 2. 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. Dorsal profile of caudal peduncle straight to slightly convex. Ventral profile of trunk and caudal peduncle nearly straight. Head depressed, trapezoidal from dorsal view, wider posteriorly. Dorsal profile of head 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 small longitudinal ridge beginning at posterior nostril and making eyes fully 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 large free fold. Mouth subterminal, corners pos

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

diagnosis

Diagnosis. Trichomycterus diatropoporos is distinguishable from all congeners except T. balios, T. davisi, T. papilliferus, T. payaya, T. perkos, T. plumbeus, and T. tropeiro by the possession of I + 6 pectoral-fin rays (vs. I + 5, I + 7, or more) and the first ray of the pectoral fin not prolonged as a filament (Fig. 10; vs. the first ray of the pectoral fin prolonged as a filament). Trichomycterus diatropoporos is distinguished from T. balios, T. brachykechenos, T. davisi, T. papilliferus, T. payaya, T. perkos, T. plumbeus, T. poikilos, and T. tropeiro by the color pattern of dark blotches variable in size and shape progressively larger and coalescent dorsally thus forming extensive black pigmented regions with light yellow gaps (Fig. 10; vs. the dorsal and lateral surface of body with circular black blotches variable in size in T. balios and T. tropeiro; the dorsal and lateral surfaces of body densely mottled dark brown over a light yellow background in T. brachykechenos; head and trunk with dark brown irregularly shaped spots scattered in T. davisi; dorsal and lateral surface of body pale brown to light gray in T. payaya, dorsal and lateral surface of body gray in T. papillifer

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

discussion

Remarks. The presence of the infraorbital sensory canal is variable among the specimens of T. diatropoporos, even in specimens from same lot and of the same size (e. g., MCP 40933). Although characters related to the reduction of the sensory canal have been used in defining species and even genera in the Trichomycterinae (seeArratia, 1998), there are no additional detectable differences in morphometrics, meristics data and coloration pattern among specimens bearing or lacking pores i 1 and i 3 of infraorbital sensory canal to justify the recognition of two different species. Apparently, this variation in the presence of pores i 1 and i 3 of infraorbital sensory canal is unique among species of Trichomycterus. One specimen (MCP 22785) also from rio da Prata basin with counts, morphometrics, and color pattern similar to T. diatropoporos lacks pelvic fins and was not included in type-series. The specimen definitely is not T. tropeiro, the species from laguna dos Patos system that consistently lacks pelvic fins, but rather appears to be an anomalous individual of T. diatropoporos. Among other trichomycterines, intraspecific variation in the presence / absence of pelvic fins is also kno

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

etymology

Etymology. From the Greek diatropos meaning variable, and poros meaning pore, in reference to the variation in the presence of pores i 1 and i 3 of infraorbital sensory canal of the new species. A noun in apposition.

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