Definition of Eurypterida
: an order of extinct, usually large, aquatic arthropods that lived during the Paleozoic era, had a cephalothorax with six pairs of limbs of which the last pair were usually shaped like paddles and a tapering abdomen of 13 segments, and included the largest known arthropods, some exceeding 6 feet (1.8 meters) in length
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Origin and Etymology of eurypterida
New Latin, from Eurypterus, included genus (from eury- + -pterus) + -ida
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