Prosomapoda

{{Short description|Clade of arthropods}}

{{Automatic taxobox

| name = Prosomapoda

| taxon = Prosomapoda

| authority = Lamsdell, 2013

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

| image =

| image2 = Cryptocellus goodnighti.jpg

| image2_caption = Cryptocellus goodnighti, a ricinuleid arachnid

| subdivision_ranks = Groups

| subdivision = * †?Borchgrevinkium

• †Synziphosurina
• Planaterga
• Xiphosura

}}

Prosomapoda is a clade of euchelicerates including the groups Xiphosura (horseshoe crabs) and Planaterga (a group comprising bunodids, pseudoniscids, chasmataspidids, eurypterids and arachnids), as well as several basal synziphosurid genera.{{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}} The clade is defined by the lack of exopods (outer branches) of prosomal appendage II-V in the adult instar, where in contrast the exopods of appendage II-V are well-developed in the non-prosomapod euchelicerates Offacolus and Dibasterium.{{Cite journal|last1=Sutton|first1=Mark D.|last2=Briggs|first2=Derek E. G.|last3=Siveter|first3=David J.|last4=Siveter|first4=Derek J.|last5=Orr|first5=Patrick J.|date=2002-06-22|title=The arthropod Offacolus kingi (Chelicerata) from the Silurian of Herefordshire, England: computer based morphological reconstructions and phylogenetic affinities|url= |journal=Proceedings of the Royal Society of London. Series B: Biological Sciences|language=en|volume=269|issue=1497|pages=1195–1203|doi=10.1098/rspb.2002.1986|issn=0962-8452|pmc=1691018|pmid=12065034}}{{Cite journal|last1=Briggs|first1=Derek E. G.|last2=Siveter|first2=Derek J.|last3=Siveter|first3=David J.|last4=Sutton|first4=Mark D.|last5=Garwood|first5=Russell J.|last6=Legg|first6=David|date=2012-09-25|title=Silurian horseshoe crab illuminates the evolution of arthropod limbs|journal=Proceedings of the National Academy of Sciences|language=en|volume=109|issue=39|pages=15702–15705|doi=10.1073/pnas.1205875109|issn=0027-8424|pmc=3465403|pmid=22967511|bibcode=2012PNAS..10915702B|doi-access=free}}