Dorsolateral head muscles of the catfish families Nematogenyidae and Trichomycteridae (Siluriformes: Loricarioidei): comparative anatomy and phylogenetic analysis

Abstract

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.

A new catfish species of the genus Trichomycterus (Siluriformes: Trichomycteridae) from the río Orinoco versant of Páramo de Cruz Verde, Eastern Cordillera of Colombia

“…brachykechenos), all remaining species of Trichomycterus whose neurocrania have been described and illustrated (e.g., T. taroba Wosiacki & Garavello, 2004) show a long roughly rectangular fontanel, extending anteriorly between the posterior part of the frontals, interrupting their midline articulation, and reaching posteriorly the center of the parieto-supraoccipital. This condition is also exhibited by the other genera traditionally assigned to Trichomycterinae (Eigenmann, 1918;Arratia, 1990Arratia, , 1998Arratia et al, 1978;Datovo & Bockmann, 2010): Bullockia Arratia, Chang, Menu-Marque & Rojas, 1978;Eremophilus Humboldt, 1805;Hatcheria Eigenmann, 1909;Rhizosomichthys Miles, 1943;Scleronema Eigenmann, 1918 andSilvinichthys Arratia, 1998 (pers. obs.…”

“…However, this hypothesis has been recently challenged on the basis of new evidence (myological characters) that supports a monophyletic Trichomycterinae (including Ituglanis and Scleronema), and the critical demonstration of the invalid or ambiguous nature of the purported synapomorphies supporting the closer relationships of Ituglanis to the clade TSVSG (Datovo & Bockmann, 2010). Under this new concept of Trichomycterinae, phylogenetic position of Ituglanis remains unresolved, so a putative clade comprising Ituglanis, Trichomycterus brachykechenos, T. cachiraensis, and T. steindachneri, supported by the shared presence of a reduced posterior fontanel is a tenable working hypothesis.…”

A new species of sand-dwelling catfish, with a phylogenetic diagnosis of Pygidianops Myers (Siluriformes: Trichomycteridae: Glanapteryginae)

“…The genus Listrura is considered the sister group to the rest of the subfamily, with Glanapteryx as the sister group to Pygidianops plus Typhlobelus. Additional recent contributions relevant to the knowledge of the subfamily include the comparative anatomy of dorsolateral head muscles in Listrura and its phylogenetic placement among representatives of the major clades of Trichomycteridae (Datovo & Bockmann, 2010); morphological trends of glanapterygines (Adriaens et al, 2010), such as body elongation, reduction of appendages, of dark pigmentation and of integumentary teeth (odontodes); and the phylogenetic placement of Typhlobelus among representative trichomycterids based on molecular sequence data (Fernández & Schaefer, 2009).…”

The brain of Brycon orbignyanus (Valenciennes, 1850) (Teleostei: Characiformes: Bryconidae): gross morphology and phylogenetic considerations

“…Standard length (SL) and head length (HL) were taken point to point with digital calipers on the left side of the specimens. Specimens were stained following the musculature dissection technique proposed by Datovo & Bockmann (2010), which allows a better visualization of cranial bones and its sutures in prepared specimens without any undesirable changes caused to their brains. The brains were then removed from the braincase using a protocol specifically developed and described below for bony fishes with laterally compressed skulls, like the characiforms.…”