What could be more complicated than the whole male & female thing and you have to have one of each to reproduce? Meet Tetrahymena, one of the most simple organisms in the world. But this thing has seven different sexes. Seven.. Parents' sex doesn't even affect their offspring; it all works no matter which one does the work. The upside is they have no problem finding a mate when they meet & greet in the pond. And frankly, we're a little jealous of that last part.