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A giant isopod is any of the almost 20 species of large isopods (crustaceans distantly related to the shrimp and crabs, which are decapods) in the genus ''Bathynomus''. They are thought to be abundant in cold, deep waters of the Atlantic, Pacific and Indian Oceans.〔Lowry, J. K. and Dempsey, K. (2006). ''The giant deep-sea scavenger genus Bathynomus (Crustacea, Isopoda, Cirolanidae) in the Indo-West Pacific.'' In: Richer de Forges, B. and Justone, J.-L. (eds.), Résultats des Compagnes Musortom, vol. 24. Mémoires du Muséum National d’Histoire Naturalle, Tome 193: 163–192.〕 ''Bathynomus giganteus'', the species upon which the generitype is based, is often considered the largest isopod in the world, though other comparably poorly known species of ''Bathynomus'' may reach a similar size (e.g., ''B. kensleyi'').〔 French zoologist Alphonse Milne-Edwards was the first〔 to describe the genus in 1879 after his colleague Alexander Agassiz collected a juvenile male ''B. giganteus'' from the Gulf of Mexico; this was an exciting discovery for both scientists and the public, as at the time the idea of a lifeless or "azoic" deep ocean had only recently been refuted by the work of Sir Charles Wyville Thomson and others. No females were recovered until 1891. Giant isopods are of little interest to most commercial fisheries owing to the typical scarcity of catches and because ensnared isopods are usually scavenged beyond marketability before they are recovered. The species are noted for resemblance to the common woodlouse or pill bug, to which they are related. The few specimens caught in the Americas and Japan with baited traps are sometimes seen in public aquariums. ==Description== Giant isopods are a good example of deep-sea gigantism (''cf.'' giant squid), as they are far larger than the "typical" isopods that are up to . ''Bathynomus'' can be divided into "giant" species where the adults generally are between long and "supergiant" species where the adults generally are between .〔 One of the "supergiants", ''B. giganteus'', reaches an average length between ,〔 with a maximum weight and length of approximately and respectively. Their morphology resembles that of their terrestrial cousin, the woodlouse: their bodies are dorso-ventrally compressed, protected by a rigid, calcareous exoskeleton composed of overlapping segments. Like some woodlice, they also possess the ability to curl up into a "ball", where only the tough shell is exposed. This provides protection from predators trying to strike at the more vulnerable underside. The first shell segment is fused to the head; the most posterior segments are often fused as well, forming a "caudal shield" over the shortened abdomen (''pleon'').〔 The large eyes are compound with nearly 4,000 facets, sessile, and spaced far apart on the head. There are two pairs of antennae. The uniramous thoracic legs or ''pereiopods'' are arranged in seven pairs, the first of which are 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. The isopods are a pale lilac in colour. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Giant isopod」の詳細全文を読む スポンサード リンク
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