Editing Merostomata (section)

==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 [[Arachnid]]a.<ref>{{cite book |editor1=Richard A. Fortey |editor2=Richard H. Thomas |year=1998 |title=Arthropod relationships |series=Volume 55 of Systematics Association Series |publisher=[[Springer Verlag]] |isbn=978-0-412-75420-3 |chapter=The early history and phylogeny of the chelicerates |author1=J. A. Dunlop |author2=P. A. Selden |name-list-style=amp |pages=221–236 |chapter-url=https://books.google.com/books?id=Pj-q9eHyIx0C&pg=PA221 }} Also available as [http://homepage.mac.com/paulselden/Sites/Website/DunlopSelden1997.pdf PDF]{{dead link|date=January 2018 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Some more recent analyses suggest the grouping Merostomata is not [[monophyly|monophyletic]], with Xiphosura being basal to a [[clade]] comprising Eurypterida and Arachnida.<ref name="Tudge">{{cite book |author=Colin Tudge |year=2002 |title=The variety of life: a survey and a celebration of all the creatures that have ever lived |publisher=[[Oxford University Press]] |isbn=978-0-19-860426-6 |chapter=Spiders, scorpions, mites, eurypterids, horseshoe crabs, and sea spiders. Subphylum Chelicerata and Subphylum Pycnogonida |pages=309–326 |chapter-url=https://books.google.com/books?id=YW-2gnuU0L0C&pg=PA312}}</ref> Other recent analyses support the monophyly of this group.<ref name=Garw>{{cite journal|title=Three-dimensional reconstruction and the phylogeny of extinct chelicerate orders|first1=Russell J.|last1=Garwood|first2=Jason A.|last2=Dunlop|year=2014|journal=PeerJ|volume=2|pages=e641|doi=10.7717/peerj.641|pmid=25405073|pmc=4232842 |doi-access=free }}</ref> The Xiphosura are estimated to have diverged from the Arachnida {{Ma|480}}.<ref>{{cite journal |author1=Davide Pisani |author2=Laura L. Poling |author3=Maureen Lyons-Weiler |author4=S. Blair Hedges |year=2004 |title=The colonization of land by animals: molecular phylogeny and divergence times among arthropods |journal=[[BMC Biology]] |volume=2 |page=1 |pmc=333434  |doi=10.1186/1741-7007-2-1 |pmid=14731304 |doi-access=free }}</ref>

The shared features of the two groups traditionally grouped in the Merostomata are now thought to be retentions of primitive conditions ([[symplesiomorphy|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>{{Cite journal |last1=Ballesteros |first1=Jesús A |last2=Santibáñez-López |first2=Carlos E |last3=Baker |first3=Caitlin M |last4=Benavides |first4=Ligia R |last5=Cunha |first5=Tauana J |last6=Gainett |first6=Guilherme |last7=Ontano |first7=Andrew Z |last8=Setton |first8=Emily V W |last9=Arango |first9=Claudia P |last10=Gavish-Regev |first10=Efrat |last11=Harvey |first11=Mark S |last12=Wheeler |first12=Ward C |last13=Hormiga |first13=Gustavo |last14=Giribet |first14=Gonzalo |last15=Sharma |first15=Prashant P |date=2022-02-03 |editor-last=Teeling |editor-first=Emma |title=Comprehensive Species Sampling and Sophisticated Algorithmic Approaches Refute the Monophyly of Arachnida |url=https://academic.oup.com/mbe/article/doi/10.1093/molbev/msac021/6522129 |journal=Molecular Biology and Evolution |language=en |volume=39 |issue=2 |pages=msac021 |doi=10.1093/molbev/msac021 |issn=0737-4038 |pmc=8845124 |pmid=35137183}}</ref>