Five-lined constellation fish

Bathysidus pentagrammus

William Beebe’s favourite fish he ever witnessed was the enigmatic five-lined constellation fish or the Bathysidus pentagrammus. At 1,900 ft, Beebe, and his colleague Otis Barton witnessed a school of them on August 11th, 1934 off Bermuda. 

They were round and narrow, with large eyes, and with long continuous vertical fins, and small pectoral fins. Initially not seeing any bioluminescence, they turned the bathysphere a few degrees into the penumbra of the light and saw that the fish's backs had five dazzling lines of glowing purple photophores. The middle line was straight and the two lines below and above were curved. He noted that the five-lined constellation fish heavily resembled butterfly or surgeonfish, but were obviously neither unless they were distantly related. Beebe described them as “one of the loveliest things I’ve ever seen.”