Merostomata

Merostomata is a name given to the now extinct sea scorpions (Eurypterida) and the horseshoe crabs (Xiphosura). There are four known species of horsehoe crabs still alive. James Dwight Dana introduced the name to refer to the horseshoe crabs only. Henry Woodward later extended it to refer to both taxa.

Merostomata
Reconstruction of Eurypterus (Eurypterida)
Views of Tachypleus tridentatus (Xiphosura)
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Class:	Merostomata Woodward, 1866
Orders
Order Eurypterida Order Xiphosura

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