''Themisto gaudichaudii'' is an

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 ...

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

of the

suborder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

Hyperiidea The Hyperiidea are a suborder of amphipods, small aquatic crustaceans. Unlike the other suborders of Amphipoda, hyperiids are exclusively marine and do not occur in fresh water. Hyperiids are distinguished by their large eyes and planktonic habi ...

Relatives

The 260

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of hyperiid amphipods are large-eyed and

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

ic amphipods, whereas gammarid amphipods have smaller eyes and tend to live on the sea floor. The handful of species of the genus ''Themisto'' are the most abundant of all amphipods. Unlike other hyperiids, which

parasitise Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

gelatinous animals such as

salp A salp (plural salps, also known colloquially as “sea grape”) or salpa (plural salpae or salpas) is a barrel-shaped, planktic tunicate. It moves by contracting, thereby pumping water through its gelatinous body, one of the most efficient ...

s and

jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella- ...

, ''Themisto'' swims free in the plankton, and is much sleeker and more streamlined than other amphipods. ''Themisto'' often forms dense swarms, similar to krill swarms. ''Themisto gaudichaudii'' is a voracious predator of anything smaller than itself, and occasionally of animals its own size or larger. In most places, the most abundant members of the

community are

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, which make up the bulk of the diet of ''T. gaudichaudii'', but it also eats fish larvae, chaetognaths, pteropods, juvenile krill, and anything else it comes across. The long limbs are folded against the body for swimming, and extend to catch prey in a similar way to the praying mantis.

Ecology

''T. gaudichaudii'' is the

Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...

species of the genus, ranging through the

Antarctic The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and other ...

region and further north onto Southern Hemisphere

continental shelves A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

. In many places, it is the most abundant predator in the plankton, and is often the third-most abundant member of the plankton community, after copepods and krill. ''T. gaudichaudii'' is an important prey item for predators such as the macaroni penguin and icefish, as well as many species of

seabird Seabirds (also known as marine birds) are birds that are adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same enviro ...

s, notably diving petrels.

Description

Adults in the

are normally long, and normally live for a year, although a few may survive to their second year and reach long. Adults off

Southern Africa Southern Africa is the southernmost subregion of the African continent, south of the Congo and Tanzania. The physical location is the large part of Africa to the south of the extensive Congo River basin. Southern Africa is home to a number of ...

are smaller, reaching .

Taxonomic history

''Themisto gaudichaudii'' was first described by Félix Édouard Guérin-Méneville in 1825. Since the genus was then

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

, ''T. gaudichaudii'' became the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

of the genus ''Themisto''. The type material was collected "'" (off the coast of the

Falkland Islands The Falkland Islands (; es, Islas Malvinas, link=no ) is an archipelago in the South Atlantic Ocean on the Patagonian Shelf. The principal islands are about east of South America's southern Patagonian coast and about from Cape Dubouzet ...

References

{{Taxonbar, from=Q2416767 Hyperiidea Crustaceans of the Atlantic Ocean Crustaceans of the Indian Ocean Crustaceans of the Pacific Ocean Fauna of the Southern Ocean Crustaceans described in 1825 Taxa named by Félix Édouard Guérin-Méneville