Villiform teeth present on the upper and lower jaws; infraorbital bone series complete, bones enlarged, partial cylinders with slender osseous arches, and with an enlarged sensory canal; snout relatively short; eye relatively large (diameter equal to or greater than distance between nares); anal-fin origin at isthmus. Eigenmannia vicentespelaea of Brazil is the only cave-inhabiting gym-notiform (Proudlove, 2005). Maximum length 140 cm, attained in Sternopygus macrurus.
The only known fossil, Humboldtichthys (formerly Ellisella) kirschbaumi, known from the Upper Miocene of Bolivia, belongs to this family; as with living gymnotiforms, it could regenerate its caudal skeleton (Gayet and Meunier, 2000; Albert and Crampton, 2005). Species are also known as rattail knifefishes.
Five genera, Archolaemus (1), Distocyclus (2), Eigenmannia (8), Rhabdolichops (8), and Sternopygus (9), with about 28 species (Albert, 2003a; Albert and Crampton, 2005).
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