The skeletal muscles of the dorsolateral region of the head of the Nematogenyidae and representatives of the all major clades of the Trichomycteridae are described and illustrated. A hypothesis on the phylogenetic relationships among these taxa exclusively based on the surveyed musculature is presented. The single most parsimonious cladogram obtained from the phylogenetic analysis of the 36 myological characters gathered and 35 terminal-taxa mostly agrees with the previous hypotheses of trichomycterid intrarelationships. The Copionodontinae and Trichogeninae form a monophyletic lineage that is the sistergroup to all remaining trichomycterids. The monophyly of the clades formed by Glanapteryginae plus Sarcoglanidinae; Stegophilinae plus Tridentinae plus Vandelliinae; and the assemblage comprising all of these five subfamilies (TSVSG clade) is corroborated. Two of our findings are, however, discordant with the previous prevailing hypotheses: the sister-group relationship among Tridentinae and Stegophilinae and the monophyly of the Trichomycterinae lato sensu, i.e., including the genera Scleronema and Ituglanis. In addition, the previously proposed osteological synapomorphies supporting the close affinities of Scleronema and Ituglanis with the TSVSG clade were revised, revealing that they are either invalid or ambiguous. Most of the synapomorphies herein proposed are homoplasy-free, with some of them corroborating the monophyly of weakly-supported groups, such as Stegophilinae.Os músculos esqueléticos da região dorsolateral da cabeça de Nematogenyidae e de representantes de todos os maiores clados de Trichomycteridae são descritos e ilustrados. Uma hipótese das relações filogenéticas entre estes táxons, baseada exclusivamente na musculatura estudada, é apresentada. O único cladograma mais parcimonioso obtido da análise filogenética dos 36 caracteres miológicos levantados e 35 táxons-terminais concorda com a maior parte das hipóteses anteriores de relações entre os tricomicterídeos. Copionodontinae e Trichogeninae formam uma linhagem monofilética que é grupo-irmã de todos os demais tricomicterídeos. O monofiletismo dos clados formados por Glanapteryginae mais Sarcoglanidinae; Stegophilinae mais Tridentinae mais Vandelliinae; e do agrupamento incluindo estas cinco subfamílias (clado TSVSG) é corroborado. Duas de nossas descobertas são, entretanto, discordantes com relação às hipóteses anteriores mais aceitas: a relação de grupo-irmão entre Tridentinae e Stegophilinae e o monofiletismo de Trichomycterinae lato sensu, i.e., incluindo os gêneros Scleronema e Ituglanis. Além disso, as sinapomorfias osteológicas previamente propostas suportando as relações de afinidade de Scleronema e Ituglanis com o clado TSVSG foram revisadas, revelando serem inválidas ou ambíguas. A maior parte das sinapomorfias aqui propostas são livres de homoplasias, com algumas delas corroborando o monofiletismo de grupos fracamente suportados, tais como o da subfamília Stegophilinae.

The infraclass Teleostei is a highly diversified group of bony fishes that encompasses 96% of all species of living fishes and almost half of extant vertebrates. Evolution of various morphological complexes in teleosts, particularly those involving soft anatomy, remains poorly understood. Notable among these problematic complexes is the adductor mandibulae, the muscle that provides the primary force for jaw adduction and mouth closure and whose architecture varies from a simple arrangement of two segments to an intricate complex of up to ten discrete subdivisions. The present study analyzed multiple morphological attributes of the adductor mandibulae in representatives of 53 of the 55 extant teleostean orders, as well as significant information from the literature in order to elucidate the homologies of the main subdivisions of this muscle. The traditional alphanumeric terminology applied to the four main divisions of the adductor mandibulae – A1, A2, A3, and Aω – patently fails to reflect homologous components of that muscle across the expanse of the Teleostei. Some features traditionally used as landmarks for identification of some divisions of the adductor mandibulae proved highly variable across the Teleostei; notably the insertion on the maxilla and the position of muscle components relative to the path of the ramus mandibularis trigeminus nerve. The evolutionary model of gain and loss of sections of the adductor mandibulae most commonly adopted under the alphanumeric system additionally proved ontogenetically incongruent and less parsimonious than a model of subdivision and coalescence of facial muscle sections. Results of the analysis demonstrate the impossibility of adapting the alphanumeric terminology so as to reflect homologous entities across the spectrum of teleosts. A new nomenclatural scheme is proposed in order to achieve congruence between homology and nomenclature of the adductor mandibulae components across the entire Teleostei.

Trichomycteridae is the second most diverse family of the order Siluriformes, its members are widely distributed through the freshwaters of Central and South America, exhibiting an exceptional ecological and phenotypic disparity. The most diverse subfamily, Trichomycterinae, represented mainly by the genus Trichomycterus, historically has been recognized as non-monophyletic and various characters used to unite or divide its constituents are repeatedly called into question. No comprehensive molecular phylogenetic hypothesis regarding relationships of trichomycterids has been produced, and the present study is the first extensive phylogeny for the family Trichomycteridae, based on a multilocus dataset of three mitochondrial loci and two nuclear markers (3284bp total). Our analysis has the most comprehensive taxon-sampling of the Trichomycteridae published so far, including members of all subfamilies and a vast representation of Trichomycterus diversity. Analysis of these data showed a phylogenetic hypothesis with broad agreement between the Bayesian (BI) and maximum-likelihood (ML) trees. The results provided overwhelming support for the monophyletic status of Copionodontinae, Stegophilinae, Trichomycterinae, and Vandelliinae, but not Sarcoglanidinae and Glanapteryginae. A major feature of our results is the support to the current conceptualization of Trichomycterinae, which includes Ituglanis and Scleronema and excludes the "Trichomycterus" hasemani group. Divergence time analysis based on DNA substitution rates suggested a Lower Cretaceous origin of the family and the divergence events at subfamilial level shaped by Paleogene events in the geohistory of South America. This hypothesis lays a foundation for an array of future studies of evolution and biogeography of the family.