Subphylum Chelicerata, Class Arachnida

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Compared to insects, relatively few arachnids have adapted to life in fresh water. The majority of these are mites (Acari), but a few species of spiders (Araneae) use the surface film as a hunting area, with even fewer venturing under water. Members of dozens of families of mites live on and below the water's surface in lentic and lotic habitats of all varieties, including phytotelms, hot springs, rushing rivers and deep lakes. Although invasion of fresh water has occurred dozens of times in the Acari, and include predatory, herbivorous and detritivorous species, the majority of these mites belong to the Hydrachnidiae, the 'true' water mites. Most water mites have a complex life cycle involving a larval stage parasitic on insects, and predatory nymphal and adult stages. Although there is good evidence that parasitism and predation by water mites can influence population dynamics of hosts and prey, and that they are diverse and ecologically sensitive members of freshwater communities, water mites (and other freshwater mites) are often excluded from surveys of freshwater invertebrates. In addition to providing an overview of the diversity and ecology of freshwater mites, this chapter includes methods for collection, rearing and observation that should help with future studies of the biology of these interesting and still mysterious animals.

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Thorp and Covich's Freshwater Invertebrates: Ecology and General Biology: Fourth Edition

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