Fighting to mate-flatworm penis fencing
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
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.
战斗式做爱——使用阴茎击剑的扁虫
人们在博特尼海湾的水域中发现了一使用阴茎进行击剑的新种类的扁虫。Imogine lateotentare是众多被称为牡蛎蛭的掠食者中的一种。Johnston和她在NSW大学的同事Ka-Man、Michel Beal说，尽管它们是已知的最简单的生物体，它们的行为模式却很复杂。
“它们在这些生物群落（一些生长在坚硬表面不能移动的生物）周围蠕动，伺机攻击藤壶。它们将消化液注射进猎物体内，吮吸他们的肉。”
这种不到2厘米长的扁虫是雌雄同体，这意味着他们同时拥有雄性和雌性器官。为了繁殖，它们会试图将生殖器互相插入对方体内。第一个刺穿并注入精液的扁虫会继续与其他扁虫争斗，而“失败者”则负责产卵孵化。尽管这样做爱很残酷，做为世界上最低等生物的扁虫仍然显示出它们对后代父母般的照料。“它们会坐在卵上，为它们供氧并保护它们不受掠食者攻击。对于一种在进化过程中处于底层的生物种类，这的确是很复杂的行为。”