Both species are unusual benthic predators that specialize in biting off the tails of other knifefishes, and are characterized by their greatly enlarged jaws and teeth.

The name Magosternarchus honors Dr. Francisco Mago Leccia, who has made many contributions to the study of gymnotiform knifefishes; the latter part of the name sternarchus is from the Greek sternon ("chest") and archos ("rectum"), referring to the forward placement of the urogenital opening in this group of fishes.

[2] Several studies using both morphological and genetic data, published in 2013 and later, have strongly suggested that the genus should be merged into Sternarchella (making Magosternarchus a junior synonym) and this has been followed by the Catalog of Fishes.

[6] Both species of Magnosternarchus are believed to range widely in the Amazon basin, including in the Rio Negro to at least above the confluence of the Branco River.

[2] Like other apteronid knifefishes, Magnosternarchus is capable of producing a continuous weak electrical discharge for electrolocation and electrocommunication.