metastoma

{{Short description|Abdominal plate present in some anthropods}}

{{about|the abdominal plate present in some chelicerates|the genus of land snail|Metastoma roemeri}}

{{distinguish|metasoma|Melastoma}}

File:Eurypterus anatomy.png with the general body parts of a eurypterid labelled. The metastoma can be seen between the pair of swimming paddles in the ventral view.]]

The metastoma is a ventral single plate located in the opisthosoma of non-arachnid dekatriatan chelicerates such as eurypterids,{{Cite journal|last=Tollerton|first=Victor P.|date=1989|title=Morphology, taxonomy, and classification of the order Eurypterida Burmeister, 1843|journal=Journal of Paleontology|language=en|volume=63|issue=5|pages=642–657|doi=10.1017/S0022336000041275|issn=0022-3360}} chasmataspidids{{Cite journal|url=https://www.academia.edu/28212892|title=Segmentation and tagmosis in Chelicerata|last=Dunlop|first=Jason A.|last2=Lamsdell|first2=James C.|journal=Arthropod Structure & Development|volume=46|issue=3|pages=395–418|year=2017|doi=10.1016/j.asd.2016.05.002|pmid=27240897|issn=1467-8039}} and the genus Houia.{{cite journal|url=https://www.researchgate.net/publication/280917493|title=An unusual euchelicerate linking horseshoe crabs and eurypterids, from the Lower Devonian (Lochkovian) of Yunnan, China|first1=Paul A.|last1=Selden|first2=James C.|last2=Lamsdell|first3=Liu|last3=Qi|journal=Zoologica Scripta|volume=44|issue=6|year=2015|pages=645–652|doi=10.1111/zsc.12124|doi-access=free}} The metastoma located between the base of 6th prosomal appendage pair and may had functioned as part of the animal's feeding structures. It most likely represented a fused appendage pair originated from somite 7 (first opisthosomal segment), thus homologous to the chilaria of horseshoe crab and 4th walking leg pair of sea spider. In eurypterids, the plate was typically cordate (heart-shaped) in shape, though differed in shape in some genera, such as Megalograptus.{{cite journal|last1=Caster|first1=Kenneth E.|author-link=Kenneth Edward Caster|last2=Kjellesvig-Waering|first2=Erik N.|year=1964|title=Upper Ordovician eurypterids of Ohio|url=https://www.biodiversitylibrary.org/page/10693962|journal=Paleontological Research Institution}}