New species of the miniature genus Gelanoglanis (Siluriformes: Auchenipteridae) from the Tocantins River basin (Brazil) and osteological description of G. nanonocticolus

Two new miniature translucent catfish species of the rare genus Tridens (Siluriformes: Trichomycteridae) from the Madeira River basin, northern Brazil

Two new miniature species of the trichomycterid genus Tridens are described from the Madeira River drainage, Acre and Rondônia States, Brazil. Until this work, Tridens was a monotypic genus composed solely of Tridens melanops, from the Putumayo/Içá River drainage, upper Amazonas River basin. Tridens vitreus sp.n. is known from upper and middle Madeira River drainage and differs from all other congeners by the lack of pelvic fins and girdle and by vertebra and dorsal-fin ray counts. Tridens chicomendesi sp.n. is known from Abunã River, middle Madeira River drainage and is distinguished from all other congeners by the number of vertebrae, dorsal-fin ray count and anal-fin base colouration pattern. Tr. chicomendesi sp.n. is further distinguished from T. vitreus by a combination of character states regarding the position of urogenital opening, dorsal-fin position, anal-fin position, maxillary barbel length, number of premaxillary teeth, number of dorsal-fin rays, number of anal-fin rays, number of lateral-line system pores, frontal bone anatomy, degree of ossification of maxilla, anatomy of quadrate-hyomandibular joint, size of posterodorsal process of hyomandibula, length of opercular patch of odontodes, number of interopercular odontodes, proportion of upper hypural plate cartilage relative to its area ; by the absence of a proximal, distal and ventral cartilages on ventral hypohyal; by the absence of a lateral process on basibranchial 4; by the presence of a cartilage block on the lateral process of autopalatine, the presence of a well-developed ossification on proximal margin of ventral hypohyal, the presence of hypobranchial foramen; and by the presence of an anterior cartilaginous joint between quadrate and base of posterodorsal process of hyomandibula. This work represents the first species description for the subfamily Tridentinae in more than 30 years and for the genus Tridens since its original description in 1889.

Osteology of Tucanoichthys tucano Géry and Römer, an enigmatic miniature fish from the Amazon basin, Brazil (Teleostei: Characiformes: Characidae)

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.

Phylogenetic systematics of the driftwood catfishes (Siluriformes: Auchenipteridae): a combined morphological and molecular analysis

A comprehensive phylogeny of species relationships of the Auchenipteridae is reconstructed here with a large-scale taxon sampling based on combined morphological and molecular datasets. The hypothesized phylogeny includes most species of Auchenipteridae (97 of 124 valid species) and multiple members of siluriform families as an outgroup (32 species) to embrace the diversity of forms among related catfishes. As the first large-scale phylogeny of the Auchenipteridae, comparison between taxa included information from both morphology (264 characters) and mitochondrial and nuclear molecular markers (3490 nucleotides) from five genes: coI, 16S, rag2, myh6 and SH3PX3. Trees were generated under two different optimality criteria (Maximum Parsimony and Bayesian Inference). A new classification for the family is presented herein to bring the taxonomy more in line with the new phylogenetic hypothesis. The strict consensus tree corroborates the monophyly of superfamily Doradoidea, family Auchenipteridae and its two subfamilies, Centromochlinae and Auchenipterinae. The new classification scheme proposes nine tribes in Auchenipteridae, based on the monophyly of major groups in both subfamilies. Centromochlus, Glanidium and Tatia are each recovered as paraphyletic. To maintain a monophyletic classification, some species treated as Tatia and Centromochlus are assigned to genera not previously recognized as valid.