Reconstruction of a fossil sea scorpion making Palmichnium tracks. (public signage, Carnegie Museum of Natural History, Pittsburgh, Pennsylvania, USA) The eurypterids, or sea scorpions, are an extinct group of chelicerate arthropods. They have an elongated, scorpion-like body that could reach enormous sizes (2.5 to 3 meters!), with a nonmineralizing exoskeleton composed of chitinous material. They are generally found in shallow to very shallow water marine and marginal marine facies. Classification: Animalia, Arthropoda, Chelicerata, Merostomata, Xiphosura, Eurypterida, Eurypteridae See info. at:
en.wikipedia.org/wiki/Eurypterid and
en.wikipedia.org/wiki/Palmichnium