Metastoma Explained

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. In eurypterids, the plate was typically cordate (heart-shaped) in shape, though differed in shape in some genera, such as Megalograptus.^[4]

Notes and References

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