A redescription of deep-channel ghost knifefish, Sternarchogiton preto (Gymnotiformes: Apteronotidae), with assignment to a new genus

Maxwell J Bernt,Aaron H Fronk,Kory M Evans,James S Albert

doi:10.1590/1982-0224-2019-0126

Abstract

ABSTRACT From a study of morphological and molecular datasets we determine that a species originally described as Sternarchogiton preto does not form a monophyletic group with the other valid species of Sternarchogiton including the type species, S. nattereri. Previously-published phylogenetic analyses indicate that this species is sister to a diverse clade comprised of six described apteronotid genera. We therefore place it into a new genus diagnosed by the presence of three cranial fontanels, first and second infraorbital bones independent (not fused), the absence of an ascending process on the endopterygoid, and dark brown to black pigments over the body surface and fins membranes. We additionally provide a redescription of this enigmatic species with an emphasis on its osteology, and provide the first documentation of secondary sexual dimorphism in this species.

Highlights

Sternarchogiton is a genus of weakly electric knifefishes in the family Apteronotidae established by Eigenmann in Eigenmann, Ward (1905)
The diagnosis provided in Albert (2001) listed five characters: 1) ventral margin of descending maxillary blade with a sharp angle about two thirds distance to its tip, 2) fourth hypobranchial with medial bridge, 3) posttemporal not fused with supracleithrum, 4) third postcleithrum not ossified, and 5) descending blades of anal-fin pterygiophores broad distally
Several new molecular phylogenies have recently been proposed for Apteronotidae that reveal incongruences between the inferred relationships and the established taxonomy

Summary

Introduction

Sternarchogiton is a genus of weakly electric knifefishes in the family Apteronotidae (the ghost knifefishes) established by Eigenmann in Eigenmann, Ward (1905). The diagnosis provided in Albert (2001) listed five characters: 1) ventral margin of descending maxillary blade with a sharp angle about two thirds distance to its tip, 2) fourth hypobranchial with medial bridge (here, following Hilton et al, 2007, we interpret this bone to be the second hypobranchial), 3) posttemporal not fused with supracleithrum, 4) third postcleithrum not ossified, and 5) descending blades of anal-fin pterygiophores broad distally. A modified diagnosis was proposed by Santana, Crampton (2007) with a revision of the genus and the description of two new species, S. labiatus and S. preto This revision diagnosed the genus by the following five characters: 1) descending blade of maxilla broad, with anterior shelf, 2) ventral margin of descending maxilla bone angled, 3) mandibular canal ossicles dumbbell-shaped, 4) one or two postcleithrae ossified independently, and 5) descending blades of anal-fin pterygiophores broad

Methods

Results

Conclusion