Argyropelecus hemigymnus

Argyropelecus hemigymnus

Argyropelecus hemigymnus (30 cm.) 

Thanks to Peter Rask Møller and Jørgen G. Nielsen, SNM.

This deep sea wonder also goes by the charming name of The Half-naked Hatchetfish. The body is deep and laterally extremely compressed, somewhat resembling a hatchet (with the thorax being the "blade" and the tail fin attachment being the "handle"). It feeds on zooplankton, and are globally distributed in the deep sea.

It is a small hatchetfish rarely exceeding 38 millimetres in length, and has light-producing organs on its body. These allow them to use counter-illumination to escape predators that lurk in the depths: by matching the light intensity with the light penetrating the water from above, the fish does not appear darker if seen from below.

Its large, sometimes tube-shaped eyes can collect the faintest of light and focus well on objects both close and far where light barely penetrates.