Sperm transfer in Conchostraca LeptestheriidaeLeptestheria dahalacensisRüppel, 1837, a strictly amphigonic species, occurs due to the production in males of an extremely primitive structure. This structure, analogous to spermatophores present in most Crustacea, may be observed in the lumen as thin strips of crystalline material. Shortly before mating, sperm produced in the gonads are released together with the crystalline fibres that serve as a net which helps keep the sperm compact and adherent to the male's body. The surface and shape of the so-called spermatophore is described. Mating time is partly dependent on the degree of adherence of the spermatophore to the female's body. The origin and conformation of this primitive structure is assessed in terms of its significance as an adaptive mechanism.