Gigantocypris
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''Gigantocypris'', sometimes known as giant ostracod or giant seed shrimp, is a genus of
ostracod Ostracods, or ostracodes, are a Class (biology), class of the crustacean, Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant taxon, extant) have been identified,Brandão, S.N.; Antoni ...
crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...
s in family
Cypridinidae Cypridinidae is a family of ostracods. About half of all known species are bioluminescent Bioluminescence is the emission of light during a chemiluminescence reaction by living organisms. Bioluminescence occurs in multifarious organisms r ...
, and among the most well-known members of the class Ostracoda (together with ''
Vargula hilgendorfii ''Vargula hilgendorfii'', sometimes called the sea-firefly and one of three bioluminescent species known in Japan as umi-hotaru (海蛍), is a species of ostracod crustacean. It is the only member of genus ''Vargula'' to inhabit Japanese waters; ...
''). Its members are extremely large for ostracods, measuring up to across, have a globular shape, are typically semi-transparent orange or reddish, and have a large pair of mirror-like eyes that are used to locate their small animal prey. They are found worldwide in dark, deep and cold oceans.


Range and habitat

''Gigantocypris'' are ubiquitous in open oceans around the world, ranging from tropical to
polar regions The polar regions, also called the frigid geographical zone, zones or polar zones, of Earth are Earth's polar ice caps, the regions of the planet that surround its geographical poles (the North Pole, North and South Poles), lying within the pol ...
. Although locally abundant, the distributions of the individual species are often not well known. ''Gigantocypris'' ''dracontovalis'' is found worldwide, mostly deeper than the other species. ''Gigantocypris agassizii'' is essentially a widespread Pacific species, and ''Gigantocypris muelleri'' a widespread Atlantic and
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 60th parallel south, 60° S latitude and encircling Antarctica. With a size of , it is the seco ...
species, but there are also a few possible records of the former in the Atlantic, and a few records of the latter in the Pacific and Indian oceans. ''Gigantocypris australis'' and ''Gigantocypris danae'' are only known from the Southwestern Pacific and Western Indian Ocean, respectively. ''Gigantocypris'' have been reported at depths between . They are typically found from . There are indications that young tend to occur shallower than adults. They live in water that is dark (below the
sunlight zone The photic zone (or euphotic zone, epipelagic zone, or sunlight zone) is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological ...
) and cold, less than , with most records between about . In water that is or warmer, their swimming becomes weak and erratic.


Appearance and behavior

''Gigantocypris'' include the largest ostracods, at up to across. The largest are ''G. agassizii'' and ''G. australis''. Another relatively large species is ''G. muelleri'', which reaches up to , but typically is about , with Southern Ocean individuals averaging largest. The smallest species, such as ''G. dracontovalis'', typically reach . Females grow larger than males. Their body is suspended within a semi-translucent, globular
carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...
. Depending on the exact species, living individuals typically are orange, orange-red or violet-red, but they can also be colourless. Specimens preserved in alcohol become whitish.
Calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...
is absent in their shell, and their body is fragile with a watery body that often is damaged when collected for scientific studies. They have a water content of about 95%, far above that reported for other crustaceans and more similar to
jellyfish Jellyfish, also known as sea jellies or simply jellies, are the #Life cycle, medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animal ...
. Despite living in the darkness below the sunlight zone, they are equipped with a pair of large eyes which, rather than using
lenses A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...
to focus light onto a
retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...
, use
parabolic mirror A parabolic (or paraboloid or paraboloidal) reflector (or dish or mirror) is a reflective surface used to collect or project energy such as light, sound, or radio waves. Its shape is part of a circular paraboloid, that is, the surface generated ...
s. The parabolic mirror eyes typically have a diameter of about , look out through transparent sections of the carapace, and appear silvery or golden in colour. Their eyes are the most elaborate known from ostracods, and are better at gathering light than the eyes of any other animal (although the resolution of the image produced by the eyes is likely poor). It is thought that ''Gigantocypris'' use them to find
bioluminescent Bioluminescence is the emission of light during a chemiluminescence reaction by living organisms. Bioluminescence occurs in multifarious organisms ranging from marine vertebrates and invertebrates, as well as in some fungi, microorganisms inc ...
prey animals. They are known to feed on other ostracods,
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 (living in the water column), some are benthos, benthic (living on the sedimen ...
s,
arrow worm The Chaetognatha or chaetognaths (meaning ''bristle-jaws'') are a phylum of predatory marine worms that are a major component of plankton worldwide. Commonly known as arrow worms, they are mostly pelagic; however about 20% of the known species ...
s and small fish (primarily
fish larvae Ichthyoplankton (from Greek: wikt:ἰχθύς, ἰχθύς, , "fish"; and πλαγκτός, , "drifter") are the Fish eggs, eggs and larvae of fish. They are mostly found in the sunlit zone of the water column, less than 200 metres deep, which ...
). Exactly how they catch their prey is unclear, but studies show that the outer part of their
mandibles In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...
can be extended out through the slit (opening) of their globular carapace. ''Gigantocypris'' swim by "rowing" with two featherlike antennae, each with nine long
seta In biology, setae (; seta ; ) are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae, ...
e. Another pair of long antennae, believed to be used for sensing, extend out in front of the animal when swimming. Both their swimming and sensing antennae can be retracted into the globular carapace through its slit. They have a near-neutral
buoyancy Buoyancy (), or upthrust, is the force exerted by a fluid opposing the weight of a partially or fully immersed object (which may be also be a parcel of fluid). In a column of fluid, pressure increases with depth as a result of the weight of t ...
(marginally negative, sinking) and are able to swim smoothly (not in jerks) at a relatively high speed, indicating that they are active predators. It is speculated that their relatively large heart—the largest among ostracods in both total and relative size—supports their active behavior, as well as their large eyes. When brought to the ocean surface, they have a slightly positive (floating) buoyancy, and their swimming is highly unstable and tumbling, but they are able to re-adjust to a near-neutral buoyancy and normal swimming pattern in less than a day. They change their buoyancy by adjusting the
sulphate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
content of their
haemolymph Hemolymph, or haemolymph, is a fluid, similar to the blood in invertebrates, that circulates in the inside of the arthropod's body, remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which hemolymph ce ...
. They sometimes fall prey to other animals such as
squid A squid (: squid) is a mollusc with an elongated soft body, large eyes, eight cephalopod limb, arms, and two tentacles in the orders Myopsida, Oegopsida, and Bathyteuthida (though many other molluscs within the broader Neocoleoidea are also ...
, fish like
grenadiers A grenadier ( , ; derived from the word ''grenade'') was historically an assault-specialist soldier who threw hand grenades in siege operation battles. The distinct combat function of the grenadier was established in the mid-17th century, when ...
and chub mackerels, and
prions A prion () is a misfolded protein that induces misfolding in normal variants of the same protein, leading to cellular death. Prions are responsible for prion diseases, known as transmissible spongiform encephalopathy (TSEs), which are fat ...
. The female ''Gigantocypris'' has a brood pouch, located inside the carapace, in which the eggs and embryos develop. When "born", the young resemble miniature adults. Adult males are uncommon compared to adult females.


Species

The
World Register of Marine Species The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and comprehensive catalogue and list of names of marine organisms. Content The content of the registry is edited and maintained by scien ...
recognize six valid species in the genus ''Gigantocypris''. One of these, ''G. pellucida'' (described simultaneously with ''G. agassizii'', both based on East Pacific specimens), is often not considered valid. In contrast, possibly
undescribed species In taxonomy, an undescribed taxon is a taxon (for example, a species) that has been discovered, but not yet formally described and named. The various Nomenclature Codes specify the requirements for a new taxon to be validly described and named. U ...
are known, and Atlantic and Southern Ocean ''G. muelleri'' may represent separate species. *'' Gigantocypris agassizii'' G. W. Müller, 1895 *'' Gigantocypris australis'' Poulsen, 1962 *'' Gigantocypris danae'' Poulsen, 1962 *'' Gigantocypris dracontovalis'' Cannon, 1940 *'' Gigantocypris muelleri'' Skogsberg, 1920 *'' Gigantocypris pellucida'' G. W. Müller, 1895


References


External links

* {{Taxonbar, from1=Q4021119, from2=Q130073838 Myodocopida Ostracod genera