Chromodoris reticulata and the disposable penis

Image: berniedup

Chromodoris reticulata is the nudibranch that loves 'em and leaves it.

This Indo-Pacific sea slug only reaches (4 in) long at most, but don't let its size fool you! Get your magnifying glass out and be prepared for some very impressive reproductive feats!

Image: Stephen Childs

Like many other sea slugs, its hermaphrodite. That's standard stuff in this company. Their male and female parts are both on the right side of the body, so in order to mate they must each face the opposite direction to get in touch with the other's sexy side.

It's a bit like sleeping head-to-toe with someone, which is weird because I thought that was supposed to stop this sort of thing.

Image: Sekizawa et al., Biology Letters
Side by side slugs, side by side penises

In any case, copulation occurs. Bits go into bobs and the couple perform an amicable sperm swap.

And then their penises fall off. Actually they wander around with their penis hanging out for about 20 minutes and THEN their penis falls off.

Image: berniedup

It sounds like an extremely unambiguous male menopause, but give it another 24 hours and they receive a shiny new penis to try out!

As it turns out, only 1 cm (0.4 in) of their penis pokes out of the body to perform the act. The whole organ is more like 3 cm (1.2 in) long, with the rest coiled up within their body. After 24 hours, this coiled part is able to make a whole new penis!

Image: Stephen Childs
Easy come, easy go, easy come again

This works for three matings, or a long, dirty weekend. After that, the coil is all used up and it's not currently known how long it takes for it to regrow.

And why do they do this? The penis is covered in backward pointing spines, possibly to remove the previously deposited sperm of rivals. It could be that all those spines make it difficult to unplug the thing from their partner's female parts.

When they said "all's fair in love and war", I didn't realise that included amputation.

.....

Check out the original paper, Sekizawa et al in Biology Letters