“Rearing up, each reveals its two-pronged penis.” Meet the creature that fences with an unusual body part

The ruffled flatworm Pseudobiceros bedfordi (also known as the Persian carpet flatworm or Bedford’s flatworm) can be hard to spot with the human eye as they make their way through the reefs of the Indo-West Pacific.

But individuals can recognise other members of their own species through their distinctive patterns, which prevents cross-species mating – and for good reason, as they have one of the most unique mating rituals in the natural world.

Like many other flatworms in its genus, the Persian carpet flatworm is hermaphroditic and capable of both fertilising eggs and injecting sperm.

Each flatworm wants to avoid the burden of looking after fertilised eggs, so any encounter between two flatworms quickly becomes a duel, with each trying to “stab and inseminate the other without being stabbed first.”

The flatworms only stop fencing once one has been impregnated, with the victor passing on its genes.