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Do nudibranchs have the best sex life of all? Or not?

Updated: Aug 28, 2023

It's been a while since I wrote a blog about sex, so here it comes (pun intended), long overdue.

I recently discovered that I am envious of nudibranchs' sex lives for the simple reason that they are both male and female and can mutually and simultaneously penetrate each other during mating (then both get to have eggs)(not for breakfast, for reproduction).

nudibranch nusapenida diving macro ladyowned
They might look cute, but they are all but vanilla...

The part 'nudi' in nudibranch comes from the word nude (nudus in Latin) since they are naked (and pretty disco psychedelic ) snails. (I wonder if nudis are seen as the naked and colourful hippies of the gastropod world...).

So these naked snails supposedly became hermaphrodites because they are pretty slow moving so if they bumped into a nudi of the same sex, they might get their rocks off but no chance of eggs. Being hermaphrodites means that all encounters cover all bases. Nature, the ingenious creator of all (cool) things, decided to make them able to both fertilize and be fertilized, all in one same small body, with the appendages of both sexes adjacent to one another for easy access in action.

nudibranch awesomediving nusapenida macro
The naked psychedelic hippies of the gastropod world...

The female portion of the reproductive system in the slugs that nudi-nerd Carissa Shipman studies includes a vagina, a receptaculum seminis (semen receptor if you don't know Latin), and glands that produce different components of the eggs. The male portion of the reproductive system includes the prostate, a vas deferens (sperm duct), and the ejaculatory duct. The two nudi 'lay' next to each other, line up their genital pores then happily copulate. Each nudi gets to be female and male simultaneously. (I am so jealous of nudis, they must have the most incredible sex ). They also have group sex, which is nice for them and makes for some interesting positions (we sometimes manage to be peeping toms on their orgies whilst diving in Nusa Penida, another good reason to come dive here if you ask me...).

Certain species of nudis also have disposable penises in an interesting evolutionary trait. They discard their penis after use, and, within 24 hours, a new one replaces it, the key is that the penis is actually really long (who knew, right?) and has a whole penile coil left inside the nudi's body that can be used at a later date. In fact, it has three of these, which is really handy in case it drops more penises along the way as it goes about its day. My take away: single-use penises: not sure if that will ever really catch on in other species, most creatures I know seem pretty attached to theirs...

Finally, the most bizarre bit (which put me off a tad of the whole nudi fetish thing all of a sudden) is that certain species inject their partner with prostate fluid in the head. Scientists are still trying to work out why they do this. Several species of snails and insects will store their sperm in their mate's body in odd places for future use but right next to the brain is a tad odd, even for slugs. Researchers hypothesize it may be some kind of mood-altering action to encourage the mate to keep and reuse a specific suitor's sperm.

nudibrach nusapenidadiving femaleowneddivecentre
Finding a mate can be time-consuming so everyone gets to fertilize and be fertilized at once...

So if you thought nudis were vanilla with their cute pompoms (rhinophores and cerata/gills) and bright colors, think again: they can mutually and simultaneously penetrate each other, they have orgies, they can chuck their penis away and they might just do a 'cephalo-traumatic secretion transfer' on their mate (i.e.'shoot their load in their partner's brain', ewww)...

I bet you'll never look at a nudi the same way now...


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