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Squat lobsters are dorsoventrally flattened crustaceans with long tails held curled beneath the thorax. They are found in the two superfamilies Galatheoidea and Chirostyloidea, which form part of the decapod infraorder Anomura, alongside groups including the hermit crabs and mole crabs. They are distributed worldwide in the oceans, and occur from near the surface to deep sea hydrothermal vents. More than 900 species have been described, in around 60 genera. Some species form dense aggregations, either on the sea floor or in the water column, and a small number are subject to commercial fishery. ==Description== The two main groups of squat lobsters share most features of their morphology. They resemble true lobsters in some ways, but are somewhat flattened dorsoventrally, and are typically smaller. Squat lobsters vary in carapace length (measured from the eye socket to the rear edge), from in the case of ''Munidopsis aries'', down to only a few millimetres in the case of ''Galathea intermedia'' and some species of ''Uroptychus''.〔 As in other decapod crustaceans, the body of a squat lobster may be divided into two main regions: the cephalothorax (itself made up of the ''cephalon'', or head, and the thorax), and the pleon or abdomen.〔 The cephalothorax is made of 13 body segments (somites), although the divisions are not obvious and are most easily inferred from the paired appendages. From front to back, these are, the two pairs of antennae, six pairs of mouthparts (mandibles, maxillae, maxillules and three pairs of maxillipeds), five pairs of pereiopods.〔 The cephalothorax is covered with a thick carapace, which may extend forwards in front of the eyes to form a rostrum; this is highly variable among squat lobsters, being vestigial in ''Chirostylus'', wide and often serrated in some genera, and long, narrow, and flanked with "supraorbital spines" in others.〔 The degree of ornamentation on the surface of the carapace also varies widely, and there are almost always at least a few setae (bristles), which can be iridescent in some members of the Galatheidae and Munididae.〔 A pair of compound eyes also project on stalks from the front of the carapace; these are made up of ommatidia with square facets, which is typical of the "reflecting superposition" form of eye. Many deep-sea species have reduced eyes, and reduced movement of the eyestalks.〔 In the families Munididae and Galatheidae, there is often a row of setae close to the eyes, forming "eyelashes".〔 The most conspicuous appendages are the pereiopods, and the largest of these is the first pair. These each end in a chela (claw), and are therefore known as the "chelipeds"; they can be more than six times the body length, although some groups show sexual dimorphism, with females having proportionally shorter chelipeds.〔 The following three pairs of pereiopods are somewhat smaller than the chelipeds and are without claws, but are otherwise similar; they are used for walking. The fifth pair of pereiopods are much smaller than the preceding pairs, and are held inconspicuously under the carapace. They each end in a tiny chela, and are generally believed to be used for cleaning the body, especially the gills, which are in a cavity protected by the carapace.〔 The pleon is made up of six somites, each bearing a pair of pleopods, and terminating in a telson. The first somite is narrower than the succeeding somites, and the last pair of pleopods are modified into uropods, which flank the telson.〔 The pleon is usually curled under the thorax, such that only the first three somites are visible from above.〔 The form of the pleopods varies between the sexes. In females, the first one or two pairs are missing, while the remaining pairs are uniramous, and have long setae, to which the eggs can be attached.〔 In males, the first two pairs are formed into gonopods, and are used to transfer the spermatophore to the female during mating; the first pair is often missing. The remaining pleopods can be similar to those of the females, or reduced in size, or entirely absent.〔 In both sexes, the uropods are biramous.〔 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「squat lobster」の詳細全文を読む スポンサード リンク
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