Giant isopod

'' Giant isopods are an example of deep-sea gigantism (cf. giant squid), as they are far larger than other isopod groups. Bathynomus can be divided into "giant" species where the adults generally are between long and "supergiant" species where the adults are typically between . One of the supergiants, B. giganteus, reaches a typical length between ; They have two pairs of antennae. The uniramous thoracic legs or pereiopods are arranged in seven pairs, the first of which is modified into maxillipeds to manipulate and bring food to the four sets of jaws. The abdomen has five segments called pleonites, each with a pair of biramous pleopods. These are modified into swimming legs and rami, flat respiratory structures acting as gills. Giant isopods are a pale lilac or pinkish in coloration. Giant isopods like Bathynomus giganteus store substantial organic reserves in their midgut gland and fat body, with lipids forming a significant component, particularly in the fat body where triacylglycerols make up 88% of total lipids. ==Range and habitat==

Giant isopods have been recorded in the West Atlantic from the US state of Georgia to Brazil, including the Gulf of Mexico and the Caribbean. The remaining Bathynomus species are all restricted to the Indo-Pacific. A few species from this genus have been reported from shallower depths, notably B. miyarei between , the poorly known B. decemspinosus between , and B. doederleini as shallow as . In regions with both giant and supergiant species, the former mainly live on the continental slope, while the latter mainly live on the bathyal plain. For example, during a survey of the deep-sea fauna of Exuma Sound in the Bahamas, B. giganteus was found to be common in water between , but more abundant towards the lower temperature. In contrast, preliminary studies indicate that B. doederleinii stops feeding when the temperature falls below . This lower temperature limit may explain their absence from temperate and frigid regions where seas at the depth preferred by Bathynomus often are colder. (although some differences are seen, and they are separate species). This reduced phenotypic divergence is linked to the extremely low light levels of their habitat. ==Diet==

Giant isopods are important scavengers in the deep-sea benthic environment. They are mostly carnivorous and feed on dead whales, fish, and squid. They may also prey on slow-moving animals such as sea cucumbers, sponges, radiolarians, nematodes, and other zoobenthos, and perhaps even live fish. As food is scarce in the deep-ocean biome, giant isopods must take advantage of whatever food they have available. They are adapted to long periods of famine and have been known to survive over 5 years without food in captivity. When a significant source of food is encountered, giant isopods gorge themselves to the point that they have difficulty moving. A study examining the digestive system contents of 1651 specimens of B. giganteus found that fish were most commonly eaten, followed by cephalopods and decapods, particularly carideans and galatheids. ==Reproduction and life cycle==

Mature females develop a brood pouch or marsupium when sexually active, the pouch being formed by overlapping oostegites or brood plates grown from the medial border of the pereiopods. The young isopods emerge from the marsupium as miniatures of the adults, known as mancas. This is not a larval stage; the mancas are fully developed, lacking only the last pair of pereiopods. The relative seasonal abundance of B. giganteus mancas and juveniles suggests a peak in reproductive capacity in the autumn and winter. As of 2021 there were only two documented instances of ovigerous (egg-bearing) giant isopod females being captured. This suggests that ovigerous individuals may seclude themselves in pits dug in the ocean floor substrate and cease foraging during the incubation of the eggs. A study of B. giganteus and B. miyarei found that larger, sexually mature individuals tended to be found in shallower regions. The approximate lifespan of B. giganteus has been estimated to be 7.7 years for females and 6 years for males, and that of B. miyarei has been estimated at 6 years for females and 9 years for males. ==Relationship to humans==

Giant isopods are occasionally eaten as novelty food, such as in East Asian cuisine like ramen; in Vietnam, however, they are actively sought as a delicacy. Relative to total size, there is not very much "meat" to be harvested. Giant isopods are killed in large numbers as bycatch in the commercial fishing of other species such as the monkfish Lophius gastrophysus. During 14 industrial fishing cruises in 2001, 55,475 giant isopods were caught as bycatch. Commercial fisheries typically do not monitor the bycatch of giant isopods, making it difficult to ascertain the scale of bycatch killings. Large quantities of plastic were found during analysis of the stomach contents of three giant isopods in the Gulf of Mexico. == Classification ==

The genus currently contains the following known species: • Bathynomus affinis • Bathynomus brucei • Bathynomus bruscai • †Bathynomus civisi • Bathynomus crosnieri • Bathynomus decemspinosus • Bathynomus doederleini • Bathynomus giganteus • Bathynomus immanis • Bathynomus jamesi • Bathynomus kapala • Bathynomus keablei • Bathynomus kensleyi • †Bathynomus kominatoensis • Bathynomus lowryi • Bathynomus maxeyorum • Bathynomus miyarei • Bathynomus obtusus • Bathynomus paracelensis • Bathynomus pelor • Bathynomus propinquus (nomen dubium) • Bathynomus raksasa • Bathynomus richeri • †Bathynomus sismondai • †Bathynomus steatopigia • †Bathynomus undecimspinosus • Bathynomus vaderi • Bathynomus wilsoni • Bathynomus yucatanensis ==Fossil record==

Fossil specimens of Bathynomus are known extending back to at least the Early Oligocene (Rupelian) of Italy, with other fossils being known from Japan and Spain. == See also ==