Tuesday, September 7, 2010

The Horseshoe Crab Diaries Part Two: In Which Paul Rambles About The Awesomeness

So I'm sad because I have not been keeping up with my silent promise to myself to be slightly more active in posting. Fall is fast approaching so I'm brewing some post ideas that are autumnal. Like: why in the heck do leaves change color anyhow?

But even though I've got two days off from my "real job" as a sea star wrangler I'm having trouble finding the time for the real meat of the whole posting process: the research. So instead of posing another lousy post that's nothing but a poorly shot photograph I thought I would do some rambling about the Horseshoe Crab.

I spend a lot of time with tidepool animals and I can honestly say that hands down my absolute favorite is the HSC. I wanted to wait to write a full post until I had a nice photo of them but you can of course go to eol.org or horseshocrab.org to check out plenty of photos of them.

So why are these animals so amazing? Well, first is their ancientness. Although our North American Horseshoe crab, limulus polyphemus, does not show up in the fossil record and the genus probably only goes back about 20 million years, the basic design of the family goes back about 300-400 million years. That's older than dinosaurs by a good 100 million years or so. Heck it beats amniotic animals all together by 40 or 50 million years. For those plant evolution experts it's about the time that ferns first appeared.

And some of you may know this, but I love to point out that they are not crabs at all. Not even close. Hermit crabs aren't crabs but at least they're decapods, in the same family as lobsters, shrimp and true crabs. But the HSC isn't even slightly a crab. The story likely goes that westerners who first came to the "new world" (it really wasn't all that new...) found these things in huge numbers all along the American coast. It lives under water (for the most part) and it has a shell, a bit like a crab, so heck, it's probably a crab. Oh, and it looks like a horseshoe, I guess. (I quite get the resemblance. If I had discovered this creature rest assured that it would have a much cooler name. Like Gorgax, Lord of the Seas. Something Awesome.)

So if it's not a crab, what the heck is it then? Well it's a chelicerate, of course! That's the family that includes the arachnids, spiders and scorpions as well as a really bizarre group of animals we colloquially call "sea spiders" (they aren't really spiders at all, and many scientists are arguing they don't even belong in the chelicerata). So not only are the HSC's closest living relatives spiders but it's also the closest living relative of trilobites, those highly successful early arthropods that are such common fossil finds.

And what makes a chelicerate a chelicerate? Well, chelecirae, of course! These are little appendages that don't quite count as legs near the mouth. In spiders we call them pedipalps and they generally are used in mating, in scorpions they have evolved into claws but on the HSC they are just tiny little finger-like grasping tools to shovel food (quite literally) into the mouth.

So I think I've rambled enough for today, but check out my references for more information and I'll plan on writing another post (of course) on the HSC. There's a lot to tell. I'm trying to learn more yet about the eyes. It seems that my source was certainly correct about the number but as I read more there may be some further speculation about the exact position of those nine eyes. In the mean time, get out and enjoy nature.

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