Two exquisite new species of Hoplisoma (Siluriformes: Callichthyidae) from the rio Tapajós basin, Brazil, with a discussion on the morphology of the mesethmoid within Corydoradinae

Abstract

A crowdfunding initiative carried out by aquarists allowed us to sample tributaries of the rio Tapajós basin in the surroundings of Jacareacanga and Maués towns, Pará and Amazonas states, respectively, in the Brazilian Amazon. During this expedition, 13 Corydoradinae species were captured, from which at least five could be confirmed as new to science. In this article, we formally describe two of these species. Both new species can be distinguished from their congeners by having the following features: (I) ventral surface of trunk with small to relatively large coalescent platelets, forming a typical mosaic-like pattern, which entirely or almost entirely covers the ventral surface trunk; (II) small, whitish yellow or beige blotches at least on predorsal portion of body; and (III) a large, smoothly arched dark brown or black patch extending from anterior portion of parieto-supraoccipital towards region of interopercle, transversally crossing orbit and forming typical mask-like blotch. The new species differ, one from another, by the conspicuously different patterns of dark markings on flanks. Considering their peculiar head morphology, a broad discussion on the relation of the mesethmoid anatomy and snout shape within Corydoradinae is provided. Additionally, a discussion of the possible positive adaptive value of their color patterns is provided.