Sunday, May 13, 2007

Leaf Slugs: Solar-Powered Suckers

Three NAKED facts

Question for visitor: Do you think this looks just like a leaf? That's why it is called a leaf slug!

NF#1: Leaf slugs belong to a bigger group of animials called the sap-sucking slugs. Instead of breaking off bits of sea weed, munching and eating them, leaf slugs pierce a hole in the algae and suck out the cell contents.

NF#2: Leaf slugs are able to keep keep the algae's chloroplasts (the part that contains chlorophyll), which continue to photosynthesise inside the slug and provide the slug with additional nutrients. That's why they look so green! But don't you agree that being green allow them to blend into so nicely with the surrounding seaweed, and that predators will have a hard time finding them?

Corny Joke: If only we can do that as well, we just need to eat some vegetables and then go sun-tanning to get the nutrients we need! Problem is everyone will turn green though... Quite eerie...

NF#3: Leaf slugs are basically snails without shells. They may look soft and defenseless, but they are NOT! The white specks in its colour pattern are in fact what we call glands. These glands can secrete a milky chemical when irritated, which can make it very distasteful for its predators. It is believed they recycle the chemicals from the food they eat.

Too Much information:
Leaf slugs are not nudibranchs! They are from the order Sacoglossa, which nudibranchs are from the order Nudibranchia. Both, however, are mollusks from the same class, Gastropoda. The leaf slug we usually see on our shores is Elysia ornata (see below).

Elysia, as with all slugs, are hermaphrodites. They have both male and female reproductive organs which are located on the right side of the head.

Hints for guides:
Leaf slugs are seasonally abundant on our shores. They usually come and go with the hairy green seaweed, bryopsis, which they feed on. So if you see lots of hairy seaweeds, keep your eyes open.

Here's another species of Elysia which we see sometimes.

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