''Themisto libellula'' is a marine

amphipod Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descr ...

of the family

Hyperiidae The Hyperiidae are a family of amphipods, containing these genera: *'' Euthemisto'' Bovallius, 1887 *'' Hyperia'' Latreille ''in'' Desmarest, 1823 *'' Hyperiella'' Bovallius, 1887 *'' Hyperoche'' Bovallius, 1887 *'' Laxohyperia'' M. Vinogradov & ...

. The species lives for 2 to 3 years, and grows up to over its lifetime. They are found in large quantities in

Arctic The Arctic ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenla ...

water. In the summer, they eat more

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

s to store as fuel for the winter. During the mid-winter, they eat

copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

s, such as '' Calanus finmarchicus''. ''T. libellula'' is eaten by

cod Cod is the common name for the demersal fish genus '' Gadus'', belonging to the family Gadidae. Cod is also used as part of the common name for a number of other fish species, and one species that belongs to genus ''Gadus'' is commonly not call ...

, polar cod, and mammals at the ice edge. In the early 2000s, the population of the species began to decrease; these effects rippled through the food chain. The levels later rose in cool years, and ''T. libellula'' have moved south of the

Arctic Circle The Arctic Circle is one of the two polar circles, and the most northerly of the five major circles of latitude as shown on maps of Earth. Its southern equivalent is the Antarctic Circle. The Arctic Circle marks the southernmost latitude at w ...

. They have been observed in "mass mortalities", where millions of ''T. libellula'' wash up dead on the coast.

References

Crustaceans described in 1822 Hyperiidea {{Amphipod-stub