Thoracetron

Thoracetron is an entire plate formed by the fusion of opisthosomal tergites behind opercular tergite (free abdominal segments) in Xiphosura of the order Xiphosurida, being considered a synapomorphy for this order (Anderson & Selden, 1997). The order Xiphosurida includes all recent species of Xiphosura — the horseshoe crabs.

Fusion of opisthosomal tergites to form a thoracetron has previously been considered a characteristic of the xiphosuran superfamilies Euproopoidea Eller, 1938 and Limuloidea Zittel, 1885. Evidence was presented by Anderson & Selden (1997) that fusion also occurs in Bellinuroidea Zittel & Eastman, 1913. Giribet et al. (2005) used it in their character matrix resulting in a synapomorphy for "Limulus" and "Carcinoscorpius".

References

* Anderson, L. I. & Selden, P. A. 1997. Opisthosomal fusion and phylogeny of Palaeozoic Xiphosura. "Lethaia", 30 , 19-31
* Giribet, G., S. Richter, G.D. Edgecombe & W.C. Wheeler. 2005. The position of crustaceans within the Arthropoda -- evidence from nine molecular loci and morphology. "Crustacean Issues" 16: 307-352.