Themisto gaudichaudii
Encyclopedia
Themisto gaudichaudii is an amphipod crustacean
of the suborder Hyperiidea
.
of hyperiid amphipods are large-eyed and plankton
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
gelatinous animals such as salp
s and jellyfish
, Themisto swims free in the plankton, and is much sleeker and more streamlined than other amphipods. Themisto often form dense swarm
s, 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 plankton
community are copepod
s, which make up the bulk of the diet of T. gaudichaudii, but it also eats fish larvae, chaetognath
s, 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.
species of the genus, ranging through the Antarctic
region and further north onto Southern Hemisphere
continental shelves. In many places, Themisto gaudichaudii is the most abundant predator in the plankton, and is often the third most abundant member of the plankton community, after copepods and krill.
Themisto gaudichaudii is an important prey item for predators such as the Macaroni Penguin
and icefish
, as well as many species of seabird
s, notably diving petrel
s.
are normally 12–21 mm (0.47244094488189–0.826771653543307 ) long, and normally live for a year, although a few may survive to their second year and reach 28 mm (1.1 in) long. Adults off Southern Africa
are smaller, reaching 12 mm (0.47244094488189 in).
in 1852. Since the genus was then monotypic, T. gaudichaudii became the type species
of the genus Themisto. The type material was collected "" (off the coast of the Falkland Islands
).
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
of the suborder Hyperiidea
Hyperiidea
Hyperiidea is a suborder of amphipods, small aquatic crustaceans. Unlike the other suborders of Amphipoda, hyperiids are exclusively marine and do not occur in freshwater. Hyperiids are distinguished by their large eyes and planktonic habitat...
.
Relatives
The 260 speciesSpecies
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of hyperiid amphipods are large-eyed and plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
ic amphipods, whereas gammarid amphipods
Gammaridea
Gammaridea is a suborder of small, shrimp-like crustaceans in the order Amphipoda. It contains about 7,275 of the 7,900 described species of amphipods, in approximately 1,000 genera, divided among around 125 families. Gammaridea includes almost all freshwater amphipods , as well as many marine...
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
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...
gelatinous animals such as salp
Salp
A salp or salpa is a barrel-shaped, planktonic tunicate. It moves by contracting, thus pumping water through its gelatinous body...
s and jellyfish
Jellyfish
Jellyfish are free-swimming members of the phylum Cnidaria. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish stages in the phylum Cnidaria...
, Themisto swims free in the plankton, and is much sleeker and more streamlined than other amphipods. Themisto often form dense swarm
Swarm
Swarm behaviour, or swarming, is a collective behaviour exhibited by animals of similar size which aggregate together, perhaps milling about the same spot or perhaps moving en masse or migrating in some direction. As a term, swarming is applied particularly to insects, but can also be applied to...
s, similar to krill
Krill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
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 plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
community are copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
s, which make up the bulk of the diet of T. gaudichaudii, but it also eats fish larvae, chaetognath
Chaetognatha
Chaetognatha, meaning hair-jaws, and commonly known as arrow worms, are a phylum of predatory marine worms that are a major component of plankton worldwide. About 20% of the known species are benthic, that is belonging to the lowest zone of the ocean, or benthic zone, and can attach to algae and...
s, pteropods, juvenile krill
Krill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
and anything else it comes across. The long limbs
Arthropod leg
The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa , trochanter , femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus ,...
are folded against the body for swimming, and extend to catch prey in a similar way to the praying mantis.
Ecology
Themisto gaudichaudii is the Southern OceanSouthern Ocean
The Southern Ocean comprises the southernmost waters of the World Ocean, generally taken to be south of 60°S latitude and encircling Antarctica. It is usually regarded as the fourth-largest of the five principal oceanic divisions...
species of the genus, ranging through the Antarctic
Antarctic
The Antarctic is the region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica and the ice shelves, waters and island territories in the Southern Ocean situated south of the Antarctic Convergence...
region and further north onto Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
continental shelves. In many places, Themisto gaudichaudii is the most abundant predator in the plankton, and is often the third most abundant member of the plankton community, after copepods and krill.
Themisto gaudichaudii is an important prey item for predators such as the Macaroni Penguin
Macaroni Penguin
The Macaroni Penguin is a species of penguin found from the Subantarctic to the Antarctic Peninsula. One of six species of crested penguin, it is very closely related to the Royal Penguin, and some authorities consider the two to be a single species...
and icefish
Notothenioidei
The Antarctic icefish belong to the perciform suborder Notothenioidei and are the largely endemic, dominant fish taxa in the cold continental shelf waters surrounding Antarctica. At present, the suborder includes 8 families with 43 genera and 122 species...
, as well as many species of seabird
Seabird
Seabirds are birds that have 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 environmental problems and feeding niches have resulted in similar adaptations...
s, notably diving petrel
Diving petrel
The diving petrels are seabirds in the bird order Procellariiformes. There are four very similar species all in the family Pelecanoididae and genus Pelecanoides , distinguished only by small differences in the coloration of their plumage and their bill construction.Diving petrels are auk-like small...
s.
Description
Adults in the AntarcticAntarctic
The Antarctic is the region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica and the ice shelves, waters and island territories in the Southern Ocean situated south of the Antarctic Convergence...
are normally 12–21 mm (0.47244094488189–0.826771653543307 ) long, and normally live for a year, although a few may survive to their second year and reach 28 mm (1.1 in) long. Adults off Southern Africa
Southern Africa
Southern Africa is the southernmost region of the African continent, variably defined by geography or geopolitics. Within the region are numerous territories, including the Republic of South Africa ; nowadays, the simpler term South Africa is generally reserved for the country in English.-UN...
are smaller, reaching 12 mm (0.47244094488189 in).
Taxonomic history
Themisto gaudichaudii was first described by Félix Édouard Guérin-MénevilleFélix Édouard Guérin-Méneville
Félix Édouard Guérin-Méneville was a French entomologist.Guérin-Méneville changed his surname from Guérin in 1836. He was the author of the illustrated work Iconographie du Règne Animal de G. Cuvier 1829–1844, a complement to the work of Georges Cuvier and Pierre André Latreille, which lacked...
in 1852. Since the genus was then monotypic, T. gaudichaudii became the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
of the genus Themisto. The type material was collected "" (off the coast of the Falkland Islands
Falkland Islands
The Falkland Islands are an archipelago in the South Atlantic Ocean, located about from the coast of mainland South America. The archipelago consists of East Falkland, West Falkland and 776 lesser islands. The capital, Stanley, is on East Falkland...
).