Relationships With Other Groups
Eurypterids have traditionally been regarded as close relatives of horseshoe crabs, together forming a group called Merostomata. Subsequent studies placed eurypterids closer to the arachnids in a group called Metastomata. There has also been a prevailing idea that eurypterids are closely related to scorpions, which they resemble. This hypothesis is reflected in the common name 'sea scorpion'. More recently it has been recognised that a little-known, extinct group called Chasmataspida also shares features with Eurypterida, and the two groups were sometimes confused with one another. The most recent summary of relationships between arachnids and their relatives recognised Eurypterida, Xiphosura and Arachnida as three major groups, but was not able to resolve any shared details among them.
Read more about this topic: List Of Eurypterids
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