Metastoma

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.

This Chelicerata-related article is a stub.

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.