In this paper, we redescribe the apteronotid fish Orthosternarchus tamandua, the only species of its genus. Historically, O. tamandua was rare in collections and only limited anatomical data was available for this species. However, numerous specimens have become available recently as a result of deep-water trawls in the main channel of the Amazon River, thereby making this redescription possible. In addition to describing the external anatomy and osteology of O. tamandua, we present data on their electronic organ discharges (EODs) recorded at time of capture, and review what is known of its distribution and ecology. We describe and illustrate the osteology of O. tamandua, and in doing so, clarify many aspects of its skeleton. For instance, contrary to previous reports, O. tamandua does possess a lateral ethmoid, although it is exceptionally small. We conclude by discussing the EODs of O. tamandua in comparison to those of other apteronotids and the anatomical characters used in the support of phylogenetic hypotheses of the genus within the family Apteronotidae.