South American electric knifefishes of the genus Archolaemus (Ostariophysi, Gymnotiformes): undetected diversity in a clade of rheophiles

Abstract

Neotropical electric knifefishes of the family Sternopygidae previously considered to represent a single relatively geographically widespread and morphologically variable species, Archolaemus blax, were analysed and found to represent a complex of five species, four of which are new to science. A fifth undescribed species from the Rio São Francisco basin outside the previous known range of the genus was identified. Recognized species of Archolaemus are: A. blax, previously thought to occur in the Rio Araguari, Rio Branco, Rio Tapajós, Rio Tocantins, and Rio Xingu, but which instead proved to be endemic to the Rio Tocantins; Archolaemus ferreirai sp. nov. from the Rio Mucajaí and Rio Uraricoera in the north‐eastern portions of the Amazon basin; Archolaemus janeae sp. nov. of the Rio Xingu and the upper Rio Tapajós, both southern tributaries of the mainstream Amazon; Archolaemus luciae sp. nov. of the Rio Trombetas, Rio Jari, and Rio Tapajós basins of the eastern Amazon, and the independent Rio Araguari draining into the Atlantic Ocean north of the mouth of the Amazon; Archolaemus orientalis sp. nov. of the São Francisco basin in eastern Brazil; and Archolaemus santosi sp. nov. of the Rio Jamari in the south‐western portion of the Amazon basin. The phylogenetic placements of Archolaemus and the recently described genus Japigny relative to the other members of the Eigenmanninae are discussed. A series of synapomorphies for Archolaemus are proposed and a hypothesis of the relationships within that genus is advanced. Rheophily of all members of Archolaemus is discussed, with the genus found to be the most specious clade within the Gymnotiformes living primarily in high‐energy settings. The reported anterior projection of the dentary teeth in A. blax was found to be a consequence of postmortem displacement.

The Untold Story of the Caudal Skeleton in the Electric Eel (Ostariophysi: Gymnotiformes: Electrophorus)

“…Gymnotiforms inhabit freshwaters across the expanse from northern Argentina to southern Mexico in settings ranging from shallow, slow-flowing streams to deep rivers, with subsets of several families specialized for life in rapids and other high energy settings [3]–[6]. Species of gymnotiforms range in body size from miniatures of 50 mm total length such as Hypopygus minissimus [7] to the over 2.5 m total length of Electrophorus electricus [8]; a 50 times range notable in itself, but particularly striking in a lineage of circa only 200 species.…”

A new species of the Eigenmannia trilineata (Gymnotiformes: Sternopygidae) species group from the río Orinoco basin, Venezuela

“…Dutra et al, 2014), of which E. sayona shares none. Vari et al (2012) proposed four synapomorphies for Archolaemus, all of which are absent in E. sayona, except for the ventral surface of the upper lip porous, possibly representing a case of convergence noted another possible convergence of upper lip surface morphology between Archolaemus and an undescribed species in the E. trilineata group). In the same study, proposed six synapomorphies for Japigny, all of which are absent in E. sayona.…”

A taxonomic revision of the Neotropical electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes: Hypopomidae), with descriptions of 15 new species

“…25-63 gill filaments on first arch. Sexual dimorphism of cranial morphology absent in all species in contrast to its presence in many apteronotid taxa (Albert & Crampton, 2009;de Santana & Vari, 2010;Fernandes et al, 2002) and in the sternopygid genus Archolaemus (Vari et al, 2012).…”