According to Science News, even when in the same body; the sexes battle for dominance: When two of these small, speckled sea worms meet to mate, there's no taking turns. Each worm, 2 to 6 centimeters long, wields its pair of side-by-side penises like a weapon. One worm tries to fertilize the other by ejaculating anywhere on its partner's body, splashing it with sperm in a cocktail that dissolves flesh. After the brew eats a hole through the skin, the sperm work their way through various ti...