The Shape of Life . The First Hunter

Flatworms have both male and female sex organs in the one animal. If you think about it, that's a great way to be. If you're rare and you're looking for a mate and you're traveling alone, you don't have to meet another female or another male. You just have to meet another one. -- Leslie Newman

Dr. Newman setting up tank for filming

Video: Newman films flatworms penis fencing

We often think of animals hunting and fighting for food, but many flatworms appear to hunt and fight for mates. Each worm is hermaphroditic, containing both ovaries with eggs and testes with sperm. Some even have two penises and one or more genital pores for receiving a unique, two-tailed sperm delivered during copulation.

Using new camera technology, Marine Biologist Leslie Newman of Australia's Southern Cross University participated in filming the marine flatworm Pseudobiceros hancockanus engaging in some odd reproductive behavior -- referred to as penis fencing.

During penis fencing, each flatworm tries to pierce the skin of the other using one of its penises. The first to succeed becomes the de facto male, delivering its sperm into the other, the de facto female. For the flatworms, this contest is serious business. Mating is a fight because the worm that assumes the female role then must expend considerable energy caring for the developing eggs.

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