The bony-eared assfish (Acanthonus armatus) is a bathypelagic species of cusk-eel found in tropical and sub-tropical oceans at depths of from 1,171 to 4,415 metres (3,842 to 14,485 ft).

[9][dubious – discuss] Like many other creatures that dwell in the depths of the sea, assfish are soft and flabby with a light skeleton.

This is likely to have resulted from a lack of food and the high pressures which accompany living at such a depth, making it difficult to generate muscle and bone.

This also perhaps accounts for the "bony-eared" part, according to Gavin Hanke, curator of vertebrate zoology at the Royal British Columbia Museum.

Adam Summers, associate director at the Friday Harbor Laboratories at the University of Washington, concurs, saying onus could easily read "as a homonym of the Greek word for ass".