Delvo
Дэлво Δε&#
I think this idea was erroneously borrowed from some insect species I can't recall the name of. I think the way it worked was that the females were always clones of their mothers and the males were always clones of their fathers (with their sperm cells having taken over an ovum and completely replaced its original nucleus), which effectively made them two separate species even though they still needed to mate in order to reproduce.