Merostomata

Merostomata is a class of chelicerate arthropods that contains the extinct Eurypterida (sea scorpions) and the extant Xiphosura (horseshoe crabs). The term was originally used by James Dwight Dana to refer to Xiphosura only, but was emended by Henry Woodward to cover both groups.

Etymology

The name "Merostomata" derives from the Greek roots {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}, "thigh") and {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}, "mouth"), in reference to the animals' possession of appendages which are mouthparts at their proximal end, but swimming legs at their distal end.<ref>Template:Cite journal</ref>

History

The scientific consensus at the beginning of the 20th century was that these two marine groups were closely related, and only more distantly related to the terrestrial Arachnida.<ref>Template:Cite book Also available as PDFTemplate:Dead link</ref> Some more recent analyses suggest the grouping Merostomata is not monophyletic, with Xiphosura being basal to a clade comprising Eurypterida and Arachnida.<ref name="Tudge">Template:Cite book</ref> Other recent analyses support the monophyly of this group.<ref name=Garw>Template:Cite journal</ref> The Xiphosura are estimated to have diverged from the Arachnida Template:Ma.<ref>Template:Cite journal</ref>

The shared features of the two groups traditionally grouped in the Merostomata are now thought to be retentions of primitive conditions (symplesiomorphies), thus the name Merostomata has been recommended to be abandoned.<ref name="Tudge"/>

However, a 2022 analysis recovered the monophyly of Merostomata, as opposed to a monophyletic Arachnida, with Xiphosura as the only modern representative in a derived position, indicating the convergence of several characteristics that supposedly united the arachnids.<ref>Template:Cite journal</ref>

External links

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