NORTH AMERICAN WATER MITES OF THE GENERA PHREATOBRACHYPODA COOK AND BHARATALBIA COOK (ACARI: HYGROBATOIDEA: ATURENAE)

Morphological and distributional data are presented for the North American species of the genera Phreatobrachypoda Cook, 1963 and Bharatalbia Cook, 1967. These mites live in gravel deposits associated with riffle areas and the hyporheic zone of streams. Female adults of Phreatobrachypoda multlpora Cook are redescribed, and males of this species are described for the first time. Adults of P. robusta Cook and P. acuta Habeeb are redescribed, and males and females of these two species are correctly correlated for the first time. Male and female adults of two new species of Phreatobrachypoda are described. The male mite described as Japonaxonopsis nuiakiensis Imamura is reassigned to Phreatobrachypoda, and the name Japonaxonopsis becomes a junior synonym of Phreatobrachypoda. Two subgenera, Phreatobrachypoda (s.s.) and Ameribrachypoda subgen.nov., are proposed and diagnosed based on the morphology of the dorsal shield, genital field, and fourth pair of legs of males. A key to known species of die genus is presented. Male and female adults of two new species of Bharatalbia (Japnnalbia) are described, and the deutonymph of one of these species is correlated with adults and described. This is the first reported occurrence of this genus in North America.All North American species of Phreatobrachypoda and Bharatalbia inhabit coastal areas in Oregon and California. The highly disjunct distributions of these genera suggest that species of both were widespread throughout western North America and eastern Eurasia during the Tertiary Era, but survived the Pleistocene only in isolated temperate refugia well beyond the southern limit of glaciers.