[2] The holotype specimen, RL 1596-4, represents an incomplete fragment of the animal, preserving the posterior margin of the skull and anterior elements of the body.

Originally the name Ellisella kirschbaumi was meant to honor both American physiologist Max Mapes Ellis and German ichthyologist Frank Kirschbaum, who pioneered the research of gymnotiform growth and regeneration.

The holotype specimen preserves the right side of Humboldtichthys with a 5.5 cm long axis, including impressions of the opercle and preopercle as well as the anterior portion of the body.

Although such striations are also present in modern members of Sternopygus, they are noticeably more pronounced in Humboldtichthys and the only diagnostic feature not called into question by Albert & Fink (2007).

Fossil remains, including stomach content from previously referred specimens, confirms the presence of both small bodied characids and catfish in addition to the knifefish fauna.

Albert & Fink suggest that the specific locality where Humboldtichthys and the other knifefish remains have been found may preserve what was once a slow moving terra firma (non floodplain) stream, a common habitat for multi-species gymnotiform assemblages.