Four types of tibiotarsal chaetotaxy are observed among Willemia species. Most species display an almost complete 'poduromorph' pattern, but the three species multilobata Gers & Deharveng, arida sp.n. and buddenbrocki Hüther differ by an increasing reduction in number of setae. W arida sp. n. is described from dry habitats in Colorado, Alberta, British Columbia and Alaska.