|Image from University of Delaware|
So I've already mentioned their ancient-ness. But just how ancient are they? Well, fossils of their ancestors have been found that date back 360 million years. That's 160 million years before any dinosaurs even showed up! They have survived massive extinctions when other related species (like Trilobites) have not. Now they are found primarily on the eastern coast of the United States. More Horseshoe Crabs spawn in Delaware Bay than in any other location on a planet. (Delaware has even designated them as their State Marine Animal)
|Image from A Delmarva Odyssey|
Anyway, to learn more about Horseshoe Crabs I would highly recommend watching the aforementioned "Nature" episode. Also, check out Horseshoecrab.org, and a Horseshoe Crab site put together by the University of Delaware. Both resources provide excellent information about the history, evolution and anatomy of this interesting invertebrates. Enjoy!