Xiphosura

Order of marine chelicerates

Xiphosura (from Ancient Greek ξίφος (xíphos) 'sword' and οὐρά (ourá) 'tail', in reference to its sword-like telson) is an order of arthropods related to arachnids. They are more commonly known as horseshoe crabs (a name applied more specifically to the only extant family, Limulidae). They first appear in the fossil record in the Early Ordovician, around 480 million years ago.

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