Differences between the two classes of tardigrade can be seen
in the reproductive anatomy. In the eutardigrades paired male
sperm ducts or a single female oviduct open into a cloaca. In the
heterotardigrades, the sperm ducts and oviduct open into a ventrally
situated preanal gonopore. Mating in gonochoristic species
can be between a single female and one or more males.