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. This species grows to a length of 37.5 centimetres (14.8 in) standard length. The larvae are similar in overall form to the related gargoyle cusk, but have elongated 3rd, 4th, and 5th pectoral-fin rays. The bony-eared assfish has been distinguished, by some sources, as having the smallest brain-to-body weight ratio of any living vertebrate, with one sample brain weighing just 6 milligrams. But the ratio is closely contested by some species of lamprey and the ocean sunfish. 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.