Description of a new Pimelodella (Siluriformes: Heptapteridae) species with a discussion on the upper pectoral girdle homology of Siluriformes

Abstract

A new species of Pimelodella is described from several right-bank tributaries of the Rio Madeira basin in Amazonas and Rondônia states, Brazil. The new species differs from all congeners by the supraoccipital process not reaching the anterior nuchal plate, 43-45 total vertebrae, maxillary barbels reaching between adpressed anal-fin terminus and caudal-fin origin, epiphyseal branch of supraorbital laterosensory canal emerging as two distantly-positioned pores and a conspicuous black mark at distal third of dorsal fin, between dorsal-fin spine and third branched ray. A detailed description of the cephalic laterosensory system of the new species is provided and contrasted with other Siluriformes and Ostariophysi. A discussion regarding homology of the catfish upper pectoral girdle bones is offered in light of modifications of the postotic and supratemporal lateral-line canals. Based on the placement of the pterotic branch of the postotic canal, it is concluded that the extrascapula is fused to the pterotic in Siluriformes. Results presented herein offer an example of how lateral-line morphology can be used as a compelling source of evidence to help determine homology of cranial and upper pectoral girdle bones.

The rediscovery of Pimelodella longipinnis (Borodin, 1927), an enigmatic Atlantic Rainforest catfish species from Southeastern Brazil (Siluriformes: Heptapteridae)

“…Measurements are point-to-point distances taken with a digital caliper under a dissecting scope, following Slobodian & Pastana (2018). Body measurements are presented as proportions of Standard Length (SL) and head parts are presented as proportions of Head Length (HL) (except for measurements of barbels, which are offered as proportions of SL).…”

“…Osteological and cephalic laterosensory canals terminology follows primarily Bockmann & Miquelarena (2008), with modifications proposed by Pastana et al (2020). Nomenclature for pectoral-fin and dorsal-fin ornamentations follow Slobodian & Pastana (2018), with modifications of Kubicek et al (2019). Fading coloration marks on holotype were observed with the aid of an ultraviolet light lantern (Netto-Ferreira & Luckenbill, 2017).…”

“…Pimelodella is certainly one of the most daunting taxonomic bottlenecks in Neotropical fishes. After Eigenmann (1917) revision, few species of Pimelodella have been subject to rigorous taxonomic studies (e.g., Mees, 1983;Leiva C., 2005;Souza-Shibatta et al, 2013;Slobodian et al, 2017;Slobodian & Pastana, 2018;Conde-Saldaña et al, 2019;Cortés-Hernández et al, 2020), in such a way that most species of the genus still await proper taxonomic and geographic delimitation.…”

“…in underway, as well as a phylogenetic study of the relationships of its species (Slobodian et al, in prep.). In this present context of limited taxonomic and phylogenetic knowledge about Pimelodella, the recognition of putatively monophyletic subsets within the genus has proven to be a useful approach to describe new species (cf., Slobodian et al, 2017;Slobodian & Pastana, 2018). Despite most Pimelodella species present a long supraoccipital process (i.e., reaching the anterior nuchal plate), some species present a slightly shorter supraoccipital process that never reaches the nuchal plate.…”

Two new, remarkably colored species of the Neotropical catfish genus Cetopsorhamdia Eigenmann & Fisher, 1916 (Siluriformes, Heptapteridae) from Chapada dos Parecis, western Brazil, with an assessment of the morphological characters bearing on their phylogenetic relationships

“…4), Pimelodella Eigenmann & Eigenmann, 1888 (Bockmann & Miquelarena, 2008: fig. 21;Slobodian & Pastana, 2018: fig. 3), Rhamdella Eigenmann & Eigenmann, 1888(Miquelarena & Menni, 1999Bockmann & Miquelarena, 2008: fig.…”