Both exophthalmy and stridulating ridges, however, can not be reliably used to determine phylogenetic relationships between different species of ghost crabs. Sakai & Türkay (2013) regarded the shape of the gonopods as more suited for this. As gonopods are important in sexual reproduction, they are less likely to evolve randomly in response to the environment. Ghost crabs of the genus "Hoplocypode" can be distinguished from those in "Ocypode" by examining their gonopods. In the former, the first gonopod has a complex, hoof-shaped tip, while in the latter they are simple and curved.