Abstract
The common non-marine ostracod Cypridopsis vidua (O.F. Müller, 1776) is used as a proxy in various biological disciplines, such as (palaeo-)ecology, evolutionary biology, ecotoxicology and parasitology. This morphospecies was considered to be an obligate parthenogen. We report on the discovery of the first population of C. vidua with males from Woods Hole (MA, USA) and determine that it is a population with mixed reproduction. We describe the morphology of the males and of the sexual and asexual females. We illustrate a copula of a male and a sexual female as well insemination in a sexual female, showing that males are functional. Therefore, Cypridopsis vidua is a morphospecies with mixed reproduction, not a full apomictic parthenogen. We use, for the first time, polychromatic polarization microscope technology to illustrate soft parts of ostracods. In addition, we compare the sexual species C. bisexualis, C. okeechobei, C. howei and C. schwartzi and conclude that these species, especially the latter three, are morphologically very close to C. vidua.