''Alicella gigantea'' is the largest

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 ...

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 ...

ever observed, with some individuals reaching up to long. The average length of A. gigantea ranges from 72.5 to 141.0 millimeters, and its weight ranges from 4.2 to 45 grams Comparatively to other amphipods, the A. gigantea grows at a much faster rate. Formerly included in the family

Lysianassidae Lysianassidae is a family of marine amphipods, containing the following genera: *'' Acontiostoma'' Stebbing, 1888 *'' Alibrotus'' Milne-Edwards, 1840 *'' Allogaussia'' Schellenberg, 1926 *'' Ambasia'' Boeck, 1871 *'' Ambasiella'' Schellenberg, 1 ...

, a new family,

Alicellidae Alicellidae is a family of amphipod crustaceans, which live as scavengers in the deep sea (at depths of ), often in association with hydrothermal vent A hydrothermal vent is a fissure on the seabed from which geothermally heated water dischar ...

, was erected in 2008 for ''Alicella'' and five related genera. The species lives only at great depths; the first specimens were collected at the end of the 19th century from the Madeira Abyssal Plain, and subsequent specimens have been found in other

abyssal plain An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between and . Lying generally between the foot of a continental rise and a mid-ocean ridge, abyssal plains cover more than 50% of the Earth's surface. T ...

s of both the

Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...

and

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

s, as well as from the

Kermadec Trench The Kermadec Trench is a linear ocean trench in the south Pacific Ocean. It stretches about from the Louisville Seamount Chain in the north (26°S) to the Hikurangi Plateau in the south (37°S), north-east of New Zealand's North Island. Toget ...

in the southwest Pacific. One specimen was found in the stomach of a

black-footed albatross The black-footed albatross (''Phoebastria nigripes'') is a large seabird of the albatross family Diomedeidae from the North Pacific. All but 2.5% of the population is found among the Northwestern Hawaiian Islands. It is one of three species of al ...

, but is thought to have been dead before it was eaten. The size of this species of amphipod is hypothesized to be connected to oxygen availability. ''A. gigantea'' have gills on coxa 7 and tubiliform accessory lobes. These additional structures allow for ''A. gigantea'' to absorb more oxygen, which is a known contributor to gigantism. The size of ''A. gigantea'' also allows them to avoid being preyed on by potential predators such as '' Notoliparis kermadecensis'', a liparid that preys on smaller amphipods.

References

{{Taxonbar, from=Q2836751 Gammaridea Monotypic crustacean genera Crustaceans described in 1899 Li W, Wang F, Jiang S, Pan B, Chan J and Xu Q (2021) The Adaptive Evolution and Gigantism Mechanisms of the Hadal “Supergiant” Amphipod Alicella gigantea. Front. Mar. Sci. 8:743663. doi: 10.3389/fmars.2021.743663