Musculatura dorsolateral cefálica de Pimelodidae Swainson, 1838 (TELEOSTEI: SILURIFORMES): Descrição muscular e Implicações filogenéticas

Abstract

Siluriformes, better known as catfish, is one of the largest orders of fish found in the Amazon, comprising 15 families that contribute to its diversity. The individuals that make up this order mostly have a naked body or one covered by bony plates, either partially or completely, as well as barbels. Among the families of Siluriformes, Pimelodidae is the eighth most diverse and has around 116 valid species and 31 genera, widely distributed in the Neotropical region, with its highest occurrence in the Amazon and Orinoco basins. Over the years, many morphological and molecular studies have been conducted to better understand the relationships among the genera of Pimelodidae, and much has been discussed regarding their phylogenetic relationships. Among the morphological description works, musculature still occupies a modest place despite being the second most investigated complex in fish, focusing mainly on the muscles of the fish's dorsolateral cephalic region. In the present study, the description of the dorsolateral cephalic musculature of the genera of the family Pimelodidae was made based on 33 species. The preparation process of the specimens of the family Pimelodidae followed the protocol using Alizarin (to stain the bones), Alcian Blue (to stain the cartilages), ethyl alcohol, and glacial acetic acid. Subsequently, the skin was removed with the aid of a scalpel and magnifying glass for the observation and description of the muscles in the dorsolateral cephalic layer. After the preparation and dissection, the descriptive part of the work was done. As a result, the main muscles that compose the dorsolateral cephalic region were observed: extensor tentaculi, which act in the movement of the maxillary barb, being present exclusively in catfish; adductor mandibulae, the largest and main muscle in the dorsolateral cephalic region, which may or may not have subdivisions into pars rictalis and pars malaris; levator arcus palatini, which promotes the connection of the neurocranium to the suspensorium; and in the movement of the operculum: levator operculi, dilatator operculi, adductor operculi, and levator arcus palatini. Based on the muscular descriptions, 48 characters plus 146 osteological characters available in the literature were developed for a comprehensive analysis within the family. The tree was rooted in Goeldiella eques (Heptapteridae) and, as additional outgroup taxa, Rhamdia sp. were included. (Heptapteridae) and Pseudopimelodidae aff. buffonius (Pseudopimelodidae). The analyses recovered a more parsimonious tree with 500 steps. The already established relationships of the Pimelodidae groups were corroborated by the present analysis, and the groups were recovered based on muscular characters, as well as the monophyly of the family. The present work also included some new muscular synapomorphies for Pimelodidae. Among the muscles that provided the most information for the description of the characters are the adductor mandibulae and the extensor tentaculi, with various variations across the analyzed species.