The lateral-line system has been traditionally recognized as an important source of phylogenetic information for different groups of fishes. Although extensively studied in Siluriformes and Cypriniformes, the lateral-line system of Characiformes remained underexplored. In the present study, the anatomy of the cephalic lateral-line canals of characiforms is described in detail and a unifying terminology that considers the ontogeny and homologies of the components of this system is offered. Aspects of the arrangement of lateral-line canals, as well as the number, location and size of canal tubules and pores, resulted in the identification of novel putative synapomorphies for Characiformes and several of its subgroups. The study also revised synapomorphies previously proposed for different characiform families and provided comments on their observed distribution across the order based on extensive taxon sampling. Information from the ontogenetic studies of the cephalic lateral-line canal system and a proposal for the proper use of these data to detect truncations in the development of the lateral-line canals across the order is also offered.

More than half the ray-finned fishes and about one-quarter of all living vertebrates belong to Percomorphacea. Among its 30 orders, Stromateiformes encompass 77 species in 16 genera and six families. Stromateiform monophyly has never been tested using morphology, and it has been rejected by molecular analyses. This comprehensive revision of Stromateiformes includes all its valid genera of all percomorph families previously aligned with the order. We sampled 207 phenotypic characters in 66 terminal taxa representing 14 orders and 46 acanthopterygian families. This dataset significantly surpasses all previous phenotype-based phylogenies of Stromateiformes, which analysed only a fraction of these characters. Stromateiformes is recovered as monophyletic, supported by eight unequivocal synapomorphies. Amarsipidae is the sister group of all other Stromateiformes (= Stromateoidei). Centrolophidae is paraphyletic, with three of its genera allocated into an early-diverging clade and the other four appearing as successive sister groups to a lineage containing the remaining stromateiforms. All other stromateoid families are monophyletic, with the following cladistic arrangement: (Nomeidae (Stromateidae (Tetragonuridae, Ariommatidae))). Our analysis convincingly refutes recent molecular phylogenetic interpretations that fail to recover a monophyletic Stromateiformes. These findings call into question large-scale conclusions of percomorph relationships and trait evolution based solely on molecular data.

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.