DOI: 10.3897/vz.74.e130038

Authors: George M.T. Mattox, Flávio C. T. Lima, Ralf Britz, Camila S. Souza, Claudio Oliveira

Abstract: Abstract The miniature fish genus Priocharax currently comprises seven valid species: P. ariel, P. britzi, P. marupiara, P. nanus, P. pygmaeus, P. toledopizae and P. varii. Except for P. ariel and P. pygmaeus, all the species are endemic to Brazil. Priocharax is characterized by several paedomorphic features such as reductions in the laterosensory system, number of fin rays, and ossification of parts of the skull. The most striking reductive character of Priocharax is the larval rayless pectoral fin in which most of its ossified endoskeletal elements are absent. We describe herein two new species of Priocharax from the vicinity of Santarém municipality, Pará state, Brazil. Both new species are distinguished from each other and from congeners by a combination of morphological features (i.e., osteological, morphometric, and meristic data) and molecular information (i.e., DNA barcode). We also present an updated maximum likelihood tree which now includes all nine species of Priocharax.

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DOI: 10.3897/vz.71.e71886

Authors: George M. T. Mattox, Kevin W. Conway

Abstract: Miniaturization, the evolution of extremely small adult body size, is a common phenomenon across the lineages of freshwater fishes, especially in the Neotropics where over 200 species are considered miniature (≤26 mm in standard length [SL]). Close to 30% of all miniature Neotropical freshwater fishes belong to the family Characidae, several of which are of uncertain phylogenetic placement within the family. We investigate the skeletal anatomy of Tucanoichthys tucano, a species of uncertain phylogenetic position from the upper Rio Negro basin, reaching a maximum known size of 16.6 mm SL. The skeleton of Tucanoichthys is characterized by the complete absence of ten skeletal elements and marked reduction in size and/or complexity of others, especially those elements associated with the cephalic latero-sensory canal system. Missing elements in the skeleton of Tucanoichthys include those that develop relatively late in the ossification sequence of the non-miniature characiform Salminus brasiliensis, suggesting that their absence in Tucanoichthys can be explained by a simple scenario of developmental truncation. A number of the reductions in the skeleton of Tucanoichthys are shared with other miniature characiforms, most notably species of Priocharax and Tyttobrycon, the latter a putative close relative of Tucanoichthys based on molecular data.

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