The horseshoe crab does not have to do much to haunt your nightmares. Their hard shell hides legs and sharp tweezers, they use their long spiny tail to turn around and they bleed milky blue blood. Think less "Sebastian of The Little Mermaid" and more "Alien Facehugger".
But it turns out that horseshoe crab is not an adorable drawing of crustacean or an exotic species – in fact, scientists have now proved that crab is not a crab at all . It's an arachnid.
The horseshoe crab (Xiphosura) is already one of the most bizarre creatures in the animal kingdom. While only four species of animals have survived the modern era, some have grown to about half a meter in length, they have survived relatively unchanged for 450 million years and have suffered multiple extinctions mass extinction, which earned them the nickname "living fossil".
As Xiphosura's blood is very sensitive to toxins, scientists are also harvesting their blood (which is a nice shade of sky blue) to use to test for contamination of items like medical equipment. (The blood is so precious that researchers in Florida recently invited the public to report sightings of horseshoe crabs that mated under the next full moon .. Sorry, kids, Disney World will have to wait!)
A new research paper, published by the University of Wisconsin-Madison and first published by National Geographic, shed new light on horseshoe crab. By studying a cluster of genetic material as well as data from genome sequencing projects, the researchers traced the pedigree family line of the horseshoe crab.
Horseshoe crabs have not evolved separately from arachnids on land like spiders and scorpions. They are actually classified as aquatic arachnids.
"This part of the tree of life has always been quite difficult to solve," said Chief Researcher Jesús Ballesteros at National Geographic.
"But one of the things that was surprising in this analysis is that no matter how we processed the data, we always got the same results … the horseshoe crabs are always nested in the arachnids. [on the family tree]. "
So, if you are an arachnophobe, you can now comfortably add the horseshoe crab to your list of fears.
And if you are a human being with eyes, you probably will too.