How does it get so super green? This seaslug has nicked loads of chloroplasts! Because it hosts these chloroplasts – the microscopic organelles that normally exist in plant cells – it can get energy from sunlight.
When Elysia chlorotica eats algae, it is able to nab the mini solar power stations from the plant cells. But it’s not as simple as popping to the beach and chomping on seaweed. If only. For a start, one of its adaptations to eating algae is a specially evolved radula. Whilst the radula in the mouths of other seaslugs might be resemble a vicious cheese grater, Elysia’s enables it to sieve out the algal cell contents. And there’s more…
I read at the New Scientist website that researchers have been investigating how this creature has been able to not only steal chloroplasts – but also put them to work. You would not expect a seaslug to have the right genes and enzymes to be able to ‘operate’ the chloroplast. In fact the chloroplasts carry DNA but their genes can only produce a small fraction of the proteins essential to run all their processes. They’ve discovered that the seaslug uses genes that once belonged to algae too. But nobody knows how that happens. Was it something Elysia chlorotica was able to do alone, or was there a virus involved?
Despite finding some algal DNA in the sex cells of the supergreen seaslug – which suggests the power to drive chloroplasts could become an inherited trick one day – baby supergreen seaslugs still have to eat algae to get chloroplasts. However, after that they can go 2 weeks without eating anything!
Kleptoplasty is something I’d love to do. Seaslugs are well known as biological thieves, and often people tell you about the way they can steal stinging cells (nematocysts) from anemones or other cnidarians. Only certain types have this special mechanism. They shift the eaten stinger cells to their gill plumes (‘branchs’) which are exposed naked on the outside of the body – hence the name ‘nudibranch’ which applies to many seaslugs. Not all are nudibranchs, Elysia is an opisthobranch, in the Sacoglossa order.
Seaslugs are hermaphrodite, typical of a mollusc. Some can squirt defensive inks and mucus from glands in their skin, and some have nasty-tasting chemicals within their skin to deter predators. Surprisingly, these chemical deterrents might not be made by the seaslugs themselves, but might sometimes be taken from the food they eat, and even transformed into new substances by them. Some are dull, some camouflaged, and some amazingly colourful and patterned, as you’ll have seen in the video clips above. There are even seaslugs with a hard shell. More cool facts about nudibranchs at the Sea Slug Forum.
Thanks to the University of Maine’s symbio Elysia website for the Elysia images and video clips, and to Sven TylerK and StephenT for the other video clips. Finally, for those of you who now love seaslugs – a music video! Spanish Dancer: