Revealed: Sea slug that discards penis after sex and then regrows another

(Getty Images)

A species of sea slug that discards its penis after sex, only to regrow another one 24 hours later has astonished scientists.

Japanese researchers made the bizarre discovery after observing the mating habits of the chromodoris reticulata species collected off the coast of Japan.

They found that about 20 minutes after having sex the sea slugs' penises would drop off. Further examination revealed that a large part of the penis was tightly coiled inside the creatures, enabling them to regenerate their missing organ and mate again within 24 hours. The animals were able to repeat this process three times in succession.

The researchers also discovered that the penis was covered in spines. They suggested these could be used to remove a rival partner's sperm left after their partner's previous matings.

As if having a detachable penis wasn't unusual enough, most sea slugs are also hermaphrodites, meaning they have both male and female sexual organs which can be used at the same time.

Scientists believe this is the first known creature able to mate with what they describe as a 'disposable penis. Their findings are published in the Royal Society's Biology Letters journal.

Bernard Picton, curator of marine invertebrates at the National Museums Northern Ireland, told the BBC: "They do have very, very complicated biology - and a lot have awfully complicated things in terms of reproduction."

"I haven't seen anything like this before," he admitted.