Metridia longa is a copepod found in the Arctic, the north Atlantic, the Pacific, and surrounding waters.

[1] M. longa are bioluminescent, emitting light when mechanically,[2] electrically, or chemically disturbed.

[3] Metridia longa is found in the sub-Arctic, Arctic, north Atlantic, and the Pacific, along the coast of the Americas and Asia.

[5] It uses recently ingested food to complete and release the eggs, but it likely uses stored lipids in oogenesis.

[7] Also, in Balsfjorden, copepodite stages I through III were found to occur mostly in the top 50 metres (160 ft) of the fjord.