Sexual Dimorphism in Carapace Morphology of Carcinoplax longimanus: A Simple Discriminating Method and its Application to Fossil Specimens

Abstract

Morphological parameters of the carapace of Carcinoplax longimanus from the Sagami Bay were measured and statistically analyzed to make establish a simple sex discriminating method. Significant sexual differences in carapace aspect ratio and orbital cavity width/carapace width ratio were not detected. On the other hand, sexual differences in two abdomen morphological parameters, although not clear, were recognized. By combining these abdomen parameters, male and female are distinguished. Furthermore, we tested the utility of the present sex discriminating method for fossils, by using two Carcinoplax longimanus fossil specimens from the Lower Pleistocene Iimuro Formation, Kazusa Group. As a result, sex of both fossil specimens could be determined. The present sex discriminating method is important because it is applicable for isolated carapace of both modern and fossil Carcinoplax longimanus.