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Sunday, May 27, 2012

Creature Feature: Sea Hares.

Not enough good things can be said about sea slugs. Really, our land slugs might not be that pretty (and even then, there are a few exceptions), but sea slugs are almost uniformly gorgeous. Even if they aren't breathtakingly pretty, even species as simple as sea hares have their own unique charm.

Aplysia parvula looks quite fetching here. :)


The term "sea hare" covers a few genera, most notably Aplysia. Sea hares are closely related to snails, but the shell, if any, only covers important organs. They eat seaweed, so don't worry about getting bitten by monster slugs should you encounter one. They can be found in the warm waters of California, northern Mexico, and Florida - or, at least, the major ones can be found there. Others can be found in temperate and tropical waters around the world.

As is the norm with invertebrates, there are so many different sorts of sea hares out there that they could almost get their own month on this blog. We will try to focus on the two varieties of California sea hare, simply because they are the two most commonly used in science (Aplysia vaccaria and Aplysia californica).

Sea hares get their name from the pointy rhinophores sticking up out of their heads. They look like rabbit ears, but they aren't for hearing. They allow the slug to smell and taste. Some sea hares ever have extra projections that look like a little bunny tail, just to make the similarity even clearer. Maybe the old tales of everything on land having a parallel in the sea were not so far off, after all.



Sea hares,  like cephalopods, are capable of expelling ink to deter predators. This ink is colored dark red like blood, making it a gross-out factor for anything thinking of eating the slug. A few of them are also poisonous to dogs and fish, just in case the ink is not enough of a deterrent. A. vaccia does not have this ink; the A. californica above clearly does.

Sea hares are the largest gastropods in the world. Looking just at our two model species, A. californica can get some 30 inches (75 cm) from head to rear when fully extended. A. vaccia has topped at 99 centimeters, again when fully extended, and has been recorded at 14 kilos - that's more than 20 pounds in U.S. measurements and quite a lot of escargot.

Sea hares, specifically A. californica, are valuable model organisms in science. On the dissecting table, they have large, brightly-colored neurons that are easy for beginning students of neuroscience to pick out. Despite this simplicity, sea hares can be conditioned and taught simple tricks. The whole genome is being sequenced as we speak. It's just a tiny bit disturbing to know that some of the tricks in human cognition go all the way back to sea slugs, but at the same time, it's pretty cool.

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