Triops longicaudatus (commonly called longtail tadpole shrimp, American tadpole shrimp, or rice tadpole shrimp) is a freshwater crustacean of the order Notostraca, resembling a miniature horseshoe crab. It is characterized by an elongated, segmented body, a flattened shield-like brownish carapace covering two thirds of the thorax, and two long filaments on the abdomen. Triops refers to its three eyes, and longicaudatus refers to the elongated tail structures. Triops longicaudatus is found in freshwater ponds and pools, often in places where few higher forms of life can exist. Like its relative Triops cancriformis, the longtail tadpole shrimp is considered a living fossil because its basic prehistoric morphology has changed little in the last 70 million years, exactly matching their ancient fossils. Triops longicaudatus is one of the oldest animal species still in existence
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