Gynandromorphism in the Chydorid CLADOCERA1

A population of Pleuroxus in Lake Balaton, Hungary, formerly designated as P. balatonicus, is here considered to be a dwarf variety of P. uncinatus, in which the males resemble the females in their general morphology rather than being strongly dimorphic and in which the large females have lost the prominent teeth at the posterior-ventral angle of the shell, although these arc present in males and in smaller (younger) females. Although large dimorphic males occasionally occur in the population, bisexual reproduction apparently is accomplished primarily by the smaller sex-intergrade males. The mechanism whereby diploid female Cladocera product diploid males by parthenogenesis is as yet unknown.