You’re never too old to find yourself feeling oddly fascinated with what is arguably life’s greatest miracle – that is, the creation of new life. That’s right, we’re talking about the birds and the bees – or should we say, we’re talking about Chromodoris Reticulata, a nudibranch with a detachable penis.
Simultaneous Hermaphrodites
With its brilliant red, white, and yellow body, the Chromodoris Reticulata is a favorite with underwater photographers. This lovely little sea slug reaches a maximum length of just about four inches long, but it’s capable of some truly astonishing feats as far as reproduction is concerned. Like many other sea slug species, these nudibranchs are hermaphrodites, meaning they have both male and female reproductive organs. Both sets of organs are on the right side of the animals’ bodies so in order to mate, they face head-to-toe with one another – a little odd, considering that this is exactly the opposite of most other members of the animal kingdom.
What’s even more interesting and more exciting to scientists is that these nudibranchs don’t just exchange one set of reproductive cells – instead, they impregnate one another. That’s right, each of the sea slugs uses its male and female sexual organs simultaneously. Says Bernard Picton, who is curator of marine invertebrates at the National Museums Northern Ireland, “The penis from one fits into the female opening of the other one, and the penis from that one fits into the female opening of the first one, if you see what I mean. They are both donating sperm to the other one.” Picton is an expert in sea slug reproduction, and this intriguing behavior has him puzzled not just because of the dual exchange of reproductive material, but because of what happens next.
After the animals finish copulating, they push away from one another; a short while later, both animals shed their penises – at least, they shed the exterior portions of their penises. Picton and other researchers working on the project were astonished to see that both nudibranchs grew brand new penises within about 24 hours. After that, the whole entire cycle started over again. In all, one pair of nudibranchs sharing a tank were observed copulating 31 times.
On closer examination, it was revealed that the animals were shedding only a small exterior portion of their penises. Inside their bodies, they have large, spiral-shaped reproductive organs that continue to grow in order to replenish the missing pieces.
While orb weaving spiders, sea creatures known as periwinkles and land slugs of the genus Ariolimax are known to lose their penises after reproducing, Chromodoris Reticulata is the only known species capable of regrowing this very important appendage once it has been lost.
According to researchers, having the ability to abandon the penis and then regrow it gives some of these nudibranchs a sexual advantage over their competition. During copulation, any sperm from competing nudibranchs may be removed via a series of backward-facing spines and replaced with genetic material from the new donor, helping to ensure that the most recent mate is the one whose genes are passed on to the next generation. Said Mr. Picton, “They do have very, very complicated biology – and a lot have awfully complicated things in terms of reproduction.”