Taxonomic revision and osteology of the species complex Hemigrammus geisleri Zarske & Géry (Characiformes: Characidae)

Abstract

Hemigrammus geisleri was described based on specimens from Amazonian drainage near Óbidos, PA and Manaus, AM. It can be distinguished from the congeners by having a very characteristic coloration, which is transparent body in life, base of the anal fin with a black line, black spot on the caudal peduncle and posterior border of the dark back scales, forming a reticulated pattern. A preliminary analysis revealed the existence of at least six "morphotypes" very similar to Hemigrammus geisleri, which are widely distributed in the Amazon basin and the Orinoco and Paraguay rivers. Most of these "morphotypes" are probably new miniature species for science. This study aims to: carry out a taxonomic review of the H. geisleri species complex to understand the identity of these populations; to perform a comparative osteological study of these species with other members of Characidae, in search for unique characteristics that may help studies of kinship relations, and with the ontogenetic series of large species to evaluate if there are characters that may be related to the evolution of the miniaturization in the group. (AU)