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Sex is more about war than love for flatworms. Like all other turbellarians, they are hermaphroditic (i.e. they have both female and male genitals). The male genitals consist of two spike-like penises, which the flatworm uses both for hunting and for mating. During mating, flatworms engage in penis fencing, a duel in which each tries to impregnate the other, and the loser adopts the female role of developing the egg.