Eurypterids have the common name as 'sea scorpions,' which is what they resemble: giant, eight foot long scorpions. They are described as brown creatures with large pincers and a scorpion tail. Similar to how a cat would purr, eurypterids make a hissing sound when they are petted, as demonstrated by Fitz. Elves use eurypterids as a way of travel in Atlantis. They tow around silver carriages, similar to horses. The system is similar to a taxi system. Much to Fitz's amusement, Sophie was petrified of the eurypterid when she first had to ride one with Alden to visit Quinlin Sonden. This creature is part of the gorgodon hybrid used by Lady Gisela to guard Nightfall because of their stinging tails. Elwin owns a tunic patterned with eurypterids. At one point, Keefe also mentions going to see the eurypterid races in Atlantis, in which supposedly the eurypterids sometimes get loose and "get into the crowds and–" (he does not finish this sentence).