extinct aquatic arthropods of the Paleozoic

Eurypterida ( meaning "wide wing") are extinct carnivorous marine arthropods (segmented invertebrates with a chitinous exoskeleton and jointed legs), also called "sea scorpions." These hunters had a scorpion-like stinger which may have contained poison, 3 pairs of jointed legs, 2 clawed arms, and strong jaws. Some had two paddles for swimming. They may have swum on their backs. Eurypterids include Eurypterus, Onychopterella, Pterygotus, Mixopterus, Slimonia, Palmichnium (an ichnogenus, i.e., known from fossilized trackways), etc. Eurypterids date from the early Paleozoic Era, arising during the Ordovician period, over 400 million years ago. Many are found from the Silurian period. They went extinct in the Permian mass extinction. Eurypterids are the state fossil of New York.