How the Life-Saving Blue Blood of Horseshoe Crabs Is Extracted - The Atlantic

The unique thing about these crabs, is that they don't have hemoglobin in the traditional sense. Instead of iron, they use copper. This actually started as an academic experiment, before corporations got involved. Unfortunately, not all of the crabbies survive :(

I find it amusing (and somewhat creepy) that from the point of view of a Horseshoe Crab the whole process looks a lot like the stories that humans who claim to have been abducted by UFOs report.