An enigmatic interstitial trichomycterine catfish from south-eastern Brazil found at about 1000 km away from its sister group (Siluriformes: Trichomycteridae)

Abstract

During recent field studies in the upper Rio Paraná basin, south-eastern Brazil, a small undescribed trichomycterine catfish with interstitial habits was found. The combination of morphological character states exhibited by this species did not allow placement to any genus from eastern South America. A multigene phylogeny here performed strongly supported the new taxon as sister to Scleronema. Due to the confusing generic classification of the Trichomycterinae, the new taxon is formally placed in a new subgenus of Scleronema (Plesioscleronema subgen. nov.), instead of in a new monotypic genus. The inclusion of the new taxon in Scleronema implicated in a review of generic diagnostic morphological characters. Two apomorphic character states were found to be useful to diagnose Scleronema in this broader sense: presence of a skin flap on the posterior margin of the opercle and a unique frontal bone morphology. Scleronema auromaculatum spec. nov. differs from other trichomycterines by a unique morphology of the area involving the postero-dorsal portion of the quadrate and the adjacent region of the hyomandibula, the uroneural separated by the dorsal hypural plate by an interspace, and a widened hemal spine of the preural centre 2. The about 1000 km gap between the area where the new species was collected and the nearest collecting site of its sister group is probably a consequence of both anthropic environmental degradation and the specialised interstitial habits in this fish group, making it difficult to be found in ichthyological inventories.