No abstract

Callichthyidae comprises the subfamilies Callichthyinae and Corydoradinae, both of which are morphologically distinct and monophyletic. Although there is consensus regarding the monophyly of the family, the relationships of about 80% of its species, currently included in the genus Corydoras, remain poorly known. Despite the vast amount of osteological information for Teleostei, knowledge regarding the phylogenetic implications of encephalon anatomy is sparse and represents a poorly explored source of potential characters. The present study aims to describe the encephalon morphology in members of the Callichthyidae in order to propose new characters that may help address phylogenetic questions regarding this group. In addition to representatives of Callichthyidae, specimens belonging to the Nematogenyidae, Trichomycteridae, Scoloplacidae, Astroblepidae and Loricariidae were dissected for comparative purposes. Head dissection revealed information on the structure of the medulla spinalis, rhombencephalon, mesencephalon, diencephalon and telencephalon. The conditions observed on the encephalons examined suggest that representatives of Callichthyidae have great taste perception and processing, while Corydoradinae stand out for visual acuity and Callichthyinae for mechanoreception processing subunits. Our results also indicate that the encephalon has important features for systematic studies of the family bringing greater resolution to current phylogenetic hypotheses.

The brain gross morphology of Rhamdia quelen is described and compared with seven species of six genera of Heptapteridae. Interspecific variation in shape, size, and position of brain subdivisions was observed in all examined species. The posterior position of the hypophysis on the hypothalamus and presence of a lateral subdivision on the lobus facialis are shared by all examined heptapterids. Rhamdia quelen and Pimelodella gracilis, currently considered closely related within the family Heptapteridae, exhibit the anterior and posterior area of the telencephalon with equivalent widths, and the lateral line lobe reaching the anterior area of the lobus vagi. Members of the so called Nemuroglanis sub-clade (Cetopsorhamdia iheringi, Heptapterus mustelinus, Imparfinis mirini, and Phenacorhamdia tenebrosa) share the lobus vagi proportional smaller than the lobus facialis; the lateral line lobe reaching the half length of the lobus facialis; the tectum mesencephali in contact with the telencephalon, and thinner anterior area of the telencephalon. The results reveal several features that are phylogenetically informative among the heptapterids examined, and corroborate previous hypotheses based on other non-neural anatomical characters.

A new species of the armoured catfish genus Corydoras is described from the Xingu-Tapajos ecoregion, Brazilian Amazon. The new species can be distinguished from its congeners by having the following combination of features: short mesethmoid, with anterior tip poorly developed, smaller than 50% of bone length; posterior margin of pectoral spine with serrations directed towards spine tip or perpendicularly oriented; infraorbital 2 only in contact with sphenotic; ventral laminar expansion of infraorbital 1 poorly or moderately developed; flank midline covered by small dark brown or black saddles with similar size to remaining markings on body; relatively larger, scarcer and more sparsely distributed dark brown or black spots on body; absence of stripe on flank midline; caudal fin with conspicuous dark brown or black spots along its entire surface; slender body; and strongly narrow frontals. A more comprehensive description of poorly-explored internal character sources, such as the gross morphology of the brain, Weberian apparatus and swimbladder capsule elements is presented.