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Abstract
A detailed osteological study of the poorly known and critical endangered ghost knifefish, Tembeassu marauna, from the rio Paraná, Brazil, was conducted using X-ray microcomputed tomography (μCT scan). A redescription of the external anatomy was performed, including the unusual presence of a rostral patch of extra teeth on the region of the upper lip anterior to the premaxilla and the prominent anterior fleshy expansions in both upper and lower lips. The newly surveyed characters were included and analyzed in light of a recent morphological data matrix for Gymnotiformes. In spite of some uncertainties that remains as to phylogenetic allocation of the genus, the most probable hypothesis is that Tembeassu is the sister group of a clade that includes Megadontognathus and Apteronotus sensu stricto. The phylogenetic analysis also supports that Tembeassu is considered a valid genus of Apteronotidae. An amended diagnosis for the genus is also provided.
Highlights
Ghost knifefishes are members of the Neotropical electric fishes family Apteronotidae, a species-rich clade with more than 100 described species included in 15 genera [1]
The monotypic Tembeassu is distinguished from all other Gymnotiformes by three autapomorphies: the presence of a rostral patch of extra teeth on the region of the upper lip anterior to the premaxilla; a prominent anterior fleshy expansions in both upper and lower lips, with length similar to the premaxillary length
[28] Figs 3–4); and a fleshy lateral lobe on the lower jaw (= “chin” lobe) hypertrophied, oval-shaped, and visible in a ventral view
Summary
Ghost knifefishes are members of the Neotropical electric fishes family Apteronotidae, a species-rich clade with more than 100 described species included in 15 genera [1]. In Central and South America, apteronotids inhabit rivers channels, streams, and rapids [6,7,8,9]. They are abundant in both number of species and biomass in deep-water channels (> 5 meter depth, e.g., [6,7,10,11]).
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