Thermosphaeroma Milleri and T. Smithi, New Sphaeromatid Isopod Crustaceans From Hot Springs in Chihuahua, Mexico, with a Review of the Genus

Thermosphaeroma milleri is described from 3 hot springs in northwestern Chihuahua, and T. smithi is described from Balneario San Diego in central Chihuahua. Supplemental descriptive notes are given for Thermosphaeroma thermophilum, from Socorro, New Mexico, and its status as an endangered species is briefly discussed. A key is given for all 5 species of Thermosphaeroma, and the probable origin of the genus from marine ancestors is considered. The presence of flabelliferans in hot springs and their absence in freshwater streams, ponds, and lakes is attributed to their inability to compete with most species of larval insects.