Descrição de um gênero novo de Stevardiinae (Characifomes: Characidae) e suas relações filogenéticas

Abstract

The Characiformes is one of the most diverse orders in the neotropical ichthyofauna. About 65% of its species are included in the Characidae family. Stevardiinae is one of the 13 Characidae subfamilies and its monophyletic status is well-suported by many researchers. Here in we aim to describe a new genus of Stevardiinae and understanding their phylogenetic relationships with other members of this subfamily using Cladistic methodology. The taxonomic study was carried out through the examination of 17 samples that underwent 17 measurements and 15 counts. Hypothesis of phylogenetic relationships were elaborated from analysis of 48 terminal taxa and 175 characters with basis on osteology, external morphology, and sperm ultrastructure. The ovary of a sexually mature female was checked by histological analysis revealing presence of spermatozoa. The geographic distribution of the species is the Sepotuba River, Paraguay River basin. The phylogenetic study showed that this genus is part of the Stevardiinae subfamily with sister group relationships to the genera Diapoma, Acrobrycon, Hysteronotus, Pseudocorynopoma, Corynopoma, Pterobrycon, Gephyrocharax, Chrysobrycon, Argopleura, Phenacobrycon, Ptychocharax, Iatobrycon, Tyttocharax, Xenurobrycon and Scopeocharax. This new genus may be distinguished from other genera included into the Stevardiinae by having scales of equivalent size and development in the ventral lobe of caudal fin both in the male and female individuals, except for Diapoma, Planaltina and Acrobrycon. It differs from Diapoma and Acrobrycon by showing two modified scales in the ventral lobe versus 3-6 modified scales observed in Diapoma, and 4-8 scales in Acrobrycon. Its complete lateral line is what differs it from Diapoma which has an interrupted lateral line. It also differs from Planaltina by having 5 or 6 teeth in the inner row of premaxilla and exhibiting the beginning of the dorsal fin posterior to that of anal fin, while Planaltina has only 4 teeth in the inner row of premaxilla and shows the beginning of dorsal fin parallel to that of anal fin. Sperm ultrastructure is also described for the new genus.