[1] Ellis saw O. tamandua as a close relative to Sternarchorhamphus, which has been corroborated by recent morphological and molecular analyses.

[1] One of the gymnotiforms most specialized to living in deep river channels, O. tamandua resembles fishes adapted to caves in several respects.

Their elongated, laterally compressed bodies are nearly unpigmented, appearing bright pink due to the blood underneath.

The dorsal throng (a whip-like appendage used for electroreception) is unusually long and thick, which led it to originally be described as a "very strongly developed adipose fin" by Boulenger.

Almost the entire body, except for the dorsal midline, is densely covered with flimsily attached scales, being small and circular towards the front and larger and more rectangular towards the back.

[5][6] As in other apteronotids, O. tamandua generates a continuous weak electric field for electrolocation and communication.

The monophasic waveform of these two genera is similar to the EOD of a larval Apteronotus, suggesting that it may be a paedomorphic or evolutionarily ancestral trait.