Bony-eared assfish

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). It has been found as far north as Queen Charlotte Sound off British Columbia's coast.^[7] This species grows to a length of 37.5 centimetres (14.8 in) standard length.^[6] The larvae are similar in overall form to the related gargoyle cusk, but have elongated 3rd, 4th, and 5th pectoral-fin rays.^[8]

Bony-eared assfish Temporal range: Holocene PreꞒ Ꞓ O S D C P T J K Pg N ↓
Specimen from north of New Guinea[1]
Specimen from south of Panama[2]
Conservation status
Least Concern  (IUCN 3.1)[3]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Ophidiiformes
Family:	Ophidiidae
Subfamily:	Neobythitinae
Genus:	Acanthonus Günther, 1878
Species:	A. armatus
Binomial name
Acanthonus armatus Günther, 1878[4]
Synonyms[5][6]
Acanthonus spinifer Garman, 1899[2]

The bony-eared assfish is by some sources believed to have the smallest brain-to-body weight ratio of any vertebrate.^{[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.^[10]

Etymology

The type specimen was an 11.5-inch (29 cm) individual taken by the Challenger expedition (1872–1876) north of New Guinea at a depth of 1,075 fathoms (6,450 ft; 1,966 m). It was described in 1878 by German ichthyologist Albert Günther, who gave the species its scientific name.^[4] Armatus means "armed" in Latin, likely chosen because the fish sports spines off the tip of the nose and the gills. This also perhaps accounts for the "bony-eared" part, according to Gavin Hanke, curator of vertebrate zoology at the Royal British Columbia Museum. Akanthos is Ancient Greek for "prickly", and onus could either mean "hake, a relative of cod", Hanke says, "or a donkey". 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".^[10]