A new species of Diaphanosoma Fischer, 1850 (Crustacea: Branchiopoda: Sididae) inhabits lakes of the western United States of America

Diaphanosoma edmondsoni sp. nov. (Cladocera: Sididae) is described based on material from several lakes in Washington, California, and Montana, USA. It differs from all other known species of the genus in having a specific combination of traits: a head with conspicuously protruding dorsal part, comparatively small eye shifted ventrally, specific armament of postero-ventral valve margin, lack of thorn(s) near posterior valve margin, comparatively long distal basal spine of postabdominal claws of slightly variable shape, and occasional presence of additional large spines on the claws. This is the first endemic species of the genus (and also of the family Sididae and order Ctenopoda) recorded in the western part of North America and, along with some other cladocerans, it forms a group of taxa highlighting this region as one of the regional hot-spots of endemic aquatic fauna.