Metastoma

This article is about the abdominal plate present in some chelicerates. For the genus of land snail, see Metastoma roemeri.

Not to be confused with metasoma or Melastoma.

The metastoma is a ventral single plate located in the opisthosoma of non-arachnid dekatriatan chelicerates such as eurypterids,^[1] chasmataspidids^[2] and the genus Houia.^[3] 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.^[2] In eurypterids, the plate was typically cordate (heart-shaped) in shape, though differed in shape in some genera, such as Megalograptus.^[4]

Restoration of Eurypterus with the general body parts of a eurypterid labelled. The metastoma can be seen between the pair of swimming paddles in the ventral view.

References

1. Tollerton, Victor P. (1989). "Morphology, taxonomy, and classification of the order Eurypterida Burmeister, 1843". Journal of Paleontology. 63 (5): 642–657. doi:10.1017/S0022336000041275. ISSN 0022-3360.
2. Dunlop, Jason A.; Lamsdell, James C. (2017). "Segmentation and tagmosis in Chelicerata". Arthropod Structure & Development. 46 (3): 395–418. doi:10.1016/j.asd.2016.05.002. ISSN 1467-8039. PMID 27240897.
3. Selden, Paul A.; Lamsdell, James C.; Qi, Liu (2015). "An unusual euchelicerate linking horseshoe crabs and eurypterids, from the Lower Devonian (Lochkovian) of Yunnan, China". Zoologica Scripta. 44 (6): 645–652. doi:10.1111/zsc.12124.
4. Caster, Kenneth E.; Kjellesvig-Waering, Erik N. (1964). "Upper Ordovician eurypterids of Ohio". Paleontological Research Institution.