Molecular species delimitation and description of a new species of Phenacogaster (Teleostei, Characidae) from the southern Amazon basin.

Phenacogaster is the most species-rich genus of the subfamily Characinae with 23 valid species broadly distributed in riverine systems of South America. Despite the taxonomic diversity of the genus, little has been advanced about its molecular diversity. A recent molecular phylogeny indicated the presence of undescribed species within Phenacogaster that is formally described here. We sampled 73 specimens of Phenacogaster and sequenced the mitochondrial cytochrome c oxidase subunit I (COI) gene in order to undertake species delimitation analyses and evaluate their intra- and interspecific genetic diversity. The results show the presence of 14 species, 13 of which are valid and one undescribed. The new species is known from the tributaries of the Xingu basin, the Rio das Mortes of the Araguaia basin, and the Rio Teles Pires of the Tapajós basin. It is distinguished by the incomplete lateral line, position of the humeral blotch near the pseudotympanum, and shape of the caudal-peduncle blotch. Meristic data and genetic differentiation relative to other Phenacogaster species represent strong evidence for the recognition of the new species and highlight the occurrence of an additional lineage of P.franciscoensis.

A new Moenkhausia (Characiformes: Characidae) from rio Brao Norte, rio Tapajs basin, with comments on the fish endemism of Serra do Cachimbo plateau.

A new species of Moenkhausia is described from the rio Brao Norte, a tributary of Rio Teles Pires draining the Serra do Cachimbo, rio Tapajs basin, Par, Brazil. The new species is diagnosed from all congeners, except M. moisae and M. pirauba, by having a high number of scales in the longitudinal series (4346 vs. 2341 in other Moenkhausia species). It can also be distinguished from the aforementioned species based on the combination of the following characters: a single humeral blotch, 2125 branched anal-fin rays, and a round and symmetrical caudal blotch not continuous anteriorly with the dark midlateral stripe. The new tetra herein described represents an additional, possibly endemic, taxon from the headwaters draining from Serra do Cachimbo, in the Brazilian Shield.

Anatomy and ontogenetic changes of the facial and gular musculature of the tetra Astyanax brucutu: A remarkable case of adaptation to durophagy.

Astyanax brucutu is a peculiar species of Neotropical tetra endemic from the Chapada Diamantina, a large plateau in northeastern Brazil. Individuals of this species undergo a dramatic ontogenetic shift in their diet that is accompanied by equally remarkable changes in their feeding apparatus. Whereas juveniles of A. brucutu feed mostly on algae, adults feed almost exclusively on an endemic species of hydrobiid snail and other associated living organisms that inhabit their dead shells (including infaunal invertebrates and algae). Skeletal adaptations associated with this change in diet were previously reported, but until now, the changes in the musculature remained mostly unknown. The present paper describes the facial and gular muscles, as well as the buccal ligaments of A. brucutu in different life stages, and identifies the major ontogenetic changes in these systems associated with the diet shift in the species. Such changes primarily involve expansions of specific portions of the adductor mandibulae and associated tendons and ligaments that likely represent adaptations to increase the biting power necessary to crush copious amounts of shells ingested by larger individuals of A. brucutu. Those adaptations are absent in specimens of any size of Astyanax cf. fasciatus, a sympatric congener lacking durophagous feeding habits. Anatomical comparisons and landmark-based principal components analysis (PCA) suggest that most specializations to durophagy in A. brucutu arose by peramorphosis. We also found that several of the muscular specializations of adults of A. brucutu are paralleled in species of Creagrutus and Piabina, two other characid genera distantly related to Astyanax, but that also feed on hard food items.

A new species of Astyanax (Characiformes: Characidae) from the rio de Contas basin, Bahia, Brazil

A new species of Astyanax from tributaries of the rio de Contas, Bahia, Brazil, is described. The new species differs from congeners by having three horizontal series of scales from lateral line to pelvic-fin origin and the distal margin of third infraorbital distinctly separated from vertical and horizontal limbs of preopercle, leaving a broad area not covered by superficial bones. The new species further differs from most congeners by the presence of bony hooks on all fins of mature males. Particularly from congeners occurring in rivers of the Northeastern Mata Atlântica freshwater ecoregion, it further differs by having the highest body depth just anterior to the dorsal-fin origin, 34-37 pored lateral line scales, a vertically elongated conspicuous dark humeral blotch reaching below the lateral line and a conspicuous dark wide midlateral stripe extending from the clear area on the rear of the humeral blotch to the end of middle caudal-fin rays and forming an inconspicuous blotch on caudal peduncle.(AU)

Uma espécie nova de Astyanax de tributários do rio de Contas, Bahia, Brasil, é descrita. A espécie nova difere das congêneres por ter três séries horizontais de escamas entre a linha lateral e a origem da nadadeira pélvica e margem distal do terceiro infraorbital distintamente separada dos ramos vertical e horizontal do pré-opérculo, deixando uma ampla área sem ossos superficiais. A espécie nova difere, ainda, da maioria das congêneres pela presença de ganchos ósseos em todas as nadadeiras de machos maduros. Particularmente das congêneres que ocorrem nas drenagens da Ecorregião Mata Atlântica Nordeste, difere ainda por ter a maior altura do corpo imediatamente anterior à origem da nadadeira dorsal, 34-37 escamas perfuradas na linha lateral, presença de uma mancha umeral conspícua, verticalmente alongada, ultrapassando ventralmente a linha lateral e uma faixa escura mediana lateral larga, estendendo-se da área clara após a mancha umeral até o fim dos raios medianos caudais e formando uma mancha inconspícua no pedúnculo caudal.(AU)