Dekatriata

{{Short description|Taxonomical clade}}

{{Automatic taxobox

| name = Dekatriata

| taxon = Dekatriata

| authority = Lamsdell, 2013

| fossil_range = {{Fossil range|earliest=505|Ordovician|Recent}}

| image = Eurypterus remipes (YPM IP 211408).jpg

| image_caption = Eurypterus remipes, a eurypterid

| image2 = Araneus diadematus 257107384.jpg

| image2_caption = Araneus diadematus, an arachnid

| subdivision_ranks = Groups

| subdivision = * †Houia

• †Winneshiekia
• †Chasmataspidida
• Sclerophorata
• Arachnida
• †Eurypterida

}}

Dekatriata is a clade of planatergan chelicerates including the groups Arachnida, Chasmataspidida, Eurypterida{{Cite journal|last=Lamsdell|first=James C.|date=2012-12-18|title=Revised systematics of Palaeozoic 'horseshoe crabs' and the myth of monophyletic Xiphosura|journal=Zoological Journal of the Linnean Society|language=en|volume=167|issue=1|pages=1–27|doi=10.1111/j.1096-3642.2012.00874.x|issn=0024-4082|doi-access=free}} and additionally two stem-genera Winneshiekia and Houia.{{cite journal|url=https://www.researchgate.net/publication/282127302|title=A new Ordovician arthropod from the Winneshiek Lagerstätte of Iowa (USA) reveals the ground plan of eurypterids and chasmataspidids|first1=James|last1=Lamsdell|first2=Derek E. G.|last2=Briggs|first3=Huaibao P.|last3=Liu|first4=Robert M.|last4=McKay|journal=The Science of Nature|volume=102|issue=9–10|pages=63|year=2015|doi=10.1007/s00114-015-1312-5|pmid=26391849|bibcode=2015SciNa.102...63L|s2cid=8153035}} Dekatriata is defined by an opisthosoma with 13 segments as groundplan (the number proposed to be secondarily reduced in most arachnid orders) and fused, plate-like appendages on the first opisthosomal segment (somite VII).