Eurypterids have the common name 'sea scorpions', which is what they are, giant, eight foot long scorpions. They are brown creatures with large pincers and a scorpion tail. Similar to how a cat would purr, eurypterids make a hissing sound when they are pet. Elves use eurypterids as a way of travel in Atlantis, similar to a taxi. Much to Fitz's amusement, Sophie was petrified of the eurypterid when she first had to ride in one with Alden to visit Quinlin Sonden.