Sea slugs repeatedly copulate with disposable penises
They believe this is the first creature known that can repeatedly copulate with what they describe as a "disposable penis".
BBC News - Sea slug's 'disposable penis' surprises
The Japanese team observed sea slugs that they had collected from shallow coral reefs around Japan. They saw the animals mate 31 times.The act took between a few seconds and a few minutes, after which the creatures would push away and shed their penises, leaving them on the floor of the tank.However, the researchers were surprised to discover that just 24-hours later, the sea slugs had regenerated their male organs and were able to mate again.Closer examination of the animals' anatomy revealed that the sea slugs had a large part of their penis coiled up in a spiral inside their bodies, which they would then use to replenish their missing part.The scientists also noted that the penis was equipped with spines.At most, the animals were able to copulate three times in succession, with each bout separated by about 24 hours.It was not clear once the internal penis was used up after these attempts whether the animal's sex life - at least the male part of it - was effectively over or - after a few weeks or months - the organ could regrow.