Eurypterids have the common name as 'sea scorpions', which is what they resemble: giant, eight foot long scorpions. They 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 pet. Elves use eurypterids as a way of travel in Atlantis, similar to a taxi, but is alive. They tow around carriages, similar to horses. 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.