''Themisto'' is a genus of marine amphipods in 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 & ...

. Their distribution is

cosmopolitan Cosmopolitan may refer to: Food and drink * Cosmopolitan (cocktail), also known as a "Cosmo" History * Rootless cosmopolitan, a Soviet derogatory epithet during Joseph Stalin's anti-Semitic campaign of 1949–1953 Hotels and resorts * Cosmopoli ...

Ecological role

''Themisto'' are obligate carnivores. ''

Themisto gaudichaudii ''Themisto gaudichaudii'' is an amphipod crustacean of the suborder Hyperiidea. Relatives The 260 species of hyperiid amphipods are large-eyed and planktonic amphipods, whereas gammarid amphipods have smaller eyes and tend to live on the sea fl ...

'' has been found to feed opportunistically on copepods and chaetognaths, as juveniles also on diatoms. ''Themisto'' are important prey in many

food web A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Another name for food web is consumer-resource system. Ecologists can broadly lump all life forms into one o ...

s. For example, ''Themisto gaudichaudii'' reaches high densities (up to 61 individuals/m³) in

Kerguelen The Kerguelen Islands ( or ; in French commonly ' but officially ', ), also known as the Desolation Islands (' in French), are a group of islands in the sub-Antarctic constituting one of the two exposed parts of the Kerguelen Plateau, a large ...

waters and is a major food item for

blue petrel The blue petrel (''Halobaena caerulea'') is a small seabird in the shearwater and petrel family, Procellariidae. This small petrel is the only member of the genus ''Halobaena'', but is closely allied to the prions. It is distributed across the So ...

s, thin-billed prions,

Antarctic prion The Antarctic prion (''Pachyptila desolata'') also known as the dove prion, or totorore in Māori, is the largest of the prions, a genus of small petrels of the Southern Ocean. Taxonomy The Antarctic prion was formally described in 1789 by ...

common diving petrel The common diving petrel (''Pelecanoides urinatrix''), also known as the smaller diving petrel or simply the diving petrel, is a diving petrel, one of four very similar auk-like small petrels of the southern oceans. It is native to South Atlant ...

s, and

southern rockhopper penguin The southern rockhopper penguin group (''Eudyptes chrysocome''), is a species of rockhopper penguin, that is sometimes considered distinct from the northern rockhopper penguin. It occurs in subantarctic waters of the western Pacific and Indian ...

s. In the

Barents Sea The Barents Sea ( , also ; no, Barentshavet, ; russian: Баренцево море, Barentsevo More) is a marginal sea of the Arctic Ocean, located off the northern coasts of Norway and Russia and divided between Norwegian and Russian territo ...

, '' Themisto libellula'' is very abundant in the Arctic waters and important food item for

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 ''Boreogadus saida'', known as the polar cod or as the Arctic cod, is a fish of the cod family Gadidae, related to the true cod (genus ''Gadus''). Another fish species for which both the common names Arctic cod and polar cod are used is ''Arct ...

, and marine mammals near the ice edge, whereas '' Themisto abyssorum'' is important in Atlantic/boreal waters.

Life history

''Themisto gaudichaudii'' matures at lengths between or more. Reproduction can be nearly continuous but becomes more seasonal at higher latitudes. The offspring emerging from the marsupium are in length. ''Themisto abyssorum'' has a life span of 1–2 years and reaches a maximum length of . ''Themisto libellula'' lives 2–3 years and grows to a maximum length of .

Species

There are seven recognized species: * '' Themisto abyssorum'' (Boeck, 1870) * '' Themisto australis'' (Stebbing, 1888) * '' Themisto compressa'' Goës, 1865 * ''

'' Guérin, 1825 * '' Themisto japonica'' (Bovallius, 1887) * '' Themisto libellula'' (Lichtenstein in Mandt, 1822) * '' Themisto pacifica'' (Stebbing, 1888)

References

{{Taxonbar, from=Q10696407 Hyperiidea Crustacean genera Taxa named by Félix Édouard Guérin-Méneville