Seaslugs looking for Love

The topic of sea slug reproduction can be complicated and even contradictory. While we generally think of two slugs positioning themselves side by side head to tail during copulation, followed by the creation of a colorful egg coil, which hatches into thousands of microscopic larvae, that is an oversimplification. Courtship rituals among sea slugs vary widely. Depending on the species, copulation may occur in the blink of your eye, or last for many hours. The position of individuals during copulation also varies with some groups approaching the partner from behind positioning their reproductive organs dorsally between the parapodia of the mate. This allows for the creation of mating chains seen in sea hares, and some head shield slugs. The reproductive organs also vary between groups, some with heavily armored penises and vaginas. And as far as the eggs go, there are no limits to size, shape, color, gestation and the type of larva hatched - planktonic or not. See BOW 2007.

During years of sea slug research, we have observed many examples of what appears to be copulation between different species. These are well documented but without any evidence that this sex act will result in producing eggs that will hatch into viable larva.

Marcel's photos show just how complicated sea slug reproduction can be. Here we have three species forming a mating chain. Three, not two! Chelidonura amoena, C. electra and Mariaglaja inornata. Wow. This is a perfect example of - "I can't see my mate, but its slime trail smells right." I don't know how to explain this.

Marcel's photos are crazy. I couldn't believe it when I saw them. The first thing I thought about was - "Do these guys really think this fertilization will work?" But then I came to my senses realizing that they have no idea who they were mating with. They are blind and wouldn't know one Chelidonura from another.

This is just one more example of different species mating, for whatever reason. It's the first I have seen of three species, however. Bottom line - will the fertilization be successful; will viable eggs be produced and will larva survive from this odd sexual encounter? So far, the answer is no to all three.

Marcel Tanke presently again lives in his native country, the Netherlands. He started diving during the 14 years that they lived in China and Korea. Marcel has BSAC Instructor diving level. Diving took him pretty much all over Asia and many other places. Nudibranchs became his main interest after several trips to the Philippines and Indonesia. Marcel is still using a "point and click" camera, currently Olympus TG-6.

Send Marcel email at marceltanke52@gmail.com