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Ticks are small arachnids in the order Parasitiformes. Along with mites, they constitute the subclass Acarina. Ticks are ectoparasites (external parasites), living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians. Ticks are vectors of a number of diseases that affect both humans and other animals. Despite their poor reputation among human communities, ticks may play an ecological role by ailing infirm animals and preventing overgrazing of plant resources.〔(New York Times )〕 ==Taxonomy== Of the three families of ticks, one – Nuttalliellidae – comprises a single species, ''Nuttalliella namaqua''. The remaining two families contain the hard ticks (Ixodidae) and the soft ticks (Argasidae).〔Guglielmone ''et al.'' (2010)〕〔Goddard (2008): (p. 80 )〕 Ticks are closely related to the numerous families of mites, within the subclass Acarina (see article: Mites of livestock). The Ixodidae include over 700 species. They are known as 'hard ticks' because they differ from the Argasidae in having a ラテン語:''scutum'' or hard shield. This shield generally can resist the force of a human's soft-soled footwear, especially on soft ground; it requires a hard sole on a hard surface to crush the tick. However, stepping on an engorged tick, filled with blood, kills it easily, though messily. In nymphs and adults of the Ixodidae, a prominent ラテン語:''capitulum'' (head) projects forwards from the body; in this they differ from the Argasidae.〔Molyneux (1993) (p. 6 )〕 They differ too, in their life cycle; Ixodidae that attach to a host will bite painlessly and generally unnoticed, and they remain in place until they engorge and are ready to change their skin; this process may take days or weeks. Some species drop off the host to moult in a safe place, whereas others remain on the same host and only drop off once they are ready to lay their eggs. The Argasidae are known regionally as 'soft ticks' or 'tampans'. The family includes about 200 species, but the proper composition of the genus is under review.〔 The following genera were accepted in 2010: *''Antricola'' *''Argas'' *''Nothaspis'' *''Ornithodoros'' *''Otobius''.〔 The most obvious distinctions between the Argasidae and the Ixodidae are that: * they have no ラテン語:''scutum'' and * the ラテン語:''capitulum'' is concealed beneath the body.〔 The Argasidae also differ from the Ixodidae in their habits and ecology. Many of them feed primarily on birds, though some Ornithodoros for example feed on mammals and are extremely harmful. Both groups feed rapidly, typically biting painfully and gorging within minutes and none of the species will stick to the host in the way that hard ticks do. Unlike the Ixodidae that have no fixed dwelling place except on the host, they live in sand or in crevices or similar shelters near animal dens or nests, or in human dwellings where they might come out nightly to attack roosting birds, or emerge only when they smell carbon dioxide in the breath of their hosts and emerge from the sand to attack them. Species common in North America primarily parasitise birds, and very rarely attack humans or other mammals.〔Allan (2001)〕 The family ''Nuttalliellidae'' contains only a single species, ''Nuttalliella namaqua'', a tick found in southern Africa from Tanzania to Namibia and South Africa,.〔〔Keirans ''et al.'' (1976)〕 It can be distinguished from Ixodidae ticks and Argasidae ticks by a combination of characteristics, including the position of the stigmata, lack of setae, strongly corrugated integument, and the form of the fenestrated plates.〔Roshdy ''et al.'' (1983)〕 Fossilized ticks are common. Recent hypotheses based on total-evidence approach analysis place the origin of ticks in the Cretaceous (), with most of the evolution and dispersal occurring during the Tertiary ().〔de la Fuente (2003)〕 The oldest example is an argasid (bird) tick from Cretaceous New Jersey amber. The younger Baltic and Dominican ambers have also yielded examples, all of which can be placed in living genera. 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「tick」の詳細全文を読む スポンサード リンク
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