Thylacocephala
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Thylacocephala is unique group of extinct arthropods, with possible crustacean affinities. Typically they have a large, laterally flattened carapace that encompasses the entire body. The compound eyes are typically large and bulbous and occupied a frontal notch on the carapace. They possessed three pairs of relatively large raptorial limbs and the abdomen bore a battery of small swimming limbs.