A new species of Knodus Eigenmann (Characiformes: Characidae: Stevardiinae) with comments on nuptial tubercles and gill gland in characiform fishes.

Naércio A. Menezes,Manoela M. F. Marinho,Roberto E. Reis

doi:10.1371/journal.pone.0217915

Abstract

Knodus nuptialis n. sp. is described from the Rio Curuá drainage, Rio Xingu basin, Brazil. It can be diagnosed from its congeners by having dentary teeth decreasing gradually in size posteriorly, outer premaxillary teeth row with five cusps, 12–15 branched anal-fin rays and a single humeral spot. The species presents notable sexual dimorphism consisting of densely concentrated nuptial tubercles on head, body, and fins, gill-gland, and bony hooks in the anal fin of mature males. It was found that these sexually dimorphic features are useful and functional in males of the new species only during the reproductive season and after this period, they become atrophied, and eventually disappear. The list of characiform species presenting breeding tubercles is updated and nine species and two genera of the Characidae, Deuterodon and Bryconacidnus, are for the first time reported to have breeding tubercles.

Highlights

The combination of two premaxillary tooth rows, inner row with four teeth, and caudal-fin scaled has been traditionally used to diagnose the characid genus Knodus Eigenmann, defined as being “a Bryconamericus in all but is scaled caudal” [1]
Knodus nuptialis, new species urn:lsid:zoobank.org:act:31DC2F83-99F6-4EC6-A250-A196C90AB36F Figs 1–8, Table 1 All specimens examined from Brazil, Para, Altamira, Rio 13 de Maio at Small Hydroelectric
Knodus nuptialis share the traditional morphological features that define the genus, especially the possession of scales on the caudal fin, sometimes slightly elongate extending to about two thirds over base of caudal-fin rays

Summary

Introduction

The combination of two premaxillary tooth rows, inner row with four teeth, and caudal-fin scaled has been traditionally used to diagnose the characid genus Knodus Eigenmann, defined as being “a Bryconamericus in all but is scaled caudal” [1]. In recent phylogenetic analyzes there is consensus that Knodus is not a natural assemblage as traditionally defined [5,6,7], and [6] further defined a “Knodus sensu stricto” based on molecular data, encompassing species of Knodus, Bryconamericus and Bryconadenos. Recent collecting expeditions undertaken to one of these areas in the Rio Curua, a tributary of the Rio Xingu basin, provided a new species described . The new species is described in Knodus following the traditional definition of the genus, pending further phylogenetic studies to better establish its relationships within characids

Material and methods

Results

Discussion