Redescription and morphological variability of Darwinula stevensoni (Brady & Robertson, 1870) (Crustacea, Ostracoda

The species Darwinula stevensoni is extensively redescribed. Morphological variability of both valves and soft parts is assessed in several geographically and climatically distant populations and is found to be minimal or non-existant. Only size significantly varies between populations and this can be attributed to the differences in ambient temperatures during the larval development. Number and shape of muscle scars also vary, but this both within and between populations. Valve shape and chaetotaxy of limbs are remarkably constant. One female from an Italian population has aberrant Mx2-palps, but this specimen is considered a teratological case. Earlier records of males of D. stevensoni and the taxonomic position of the infraorder Darwinulocopina within the suborder Podocopina are briefly rediscussed. A hypothesis on the biological strategy of darwinulids is tested using data on morphological variability and taxonomic diversity.