Some malacostracans have a carapace and this is particularly well developed in the decapods where it covers the entirety of both the cephalothorax and pereon (Ruppert et al. 2004). The carapace is formed by the fusion of the tergites, the dorsal exoskeletal plate of somites (Forest et al. 2000) (see exoskeleton) and provides additional protection, the most vulnerable points of an arthropod exoskeleton being the joints. In hermit crabs, which are adapted to shelter in gastropod shells or other protective coverings, hardening of the carapace is reduced (Forest et al. 2000), allowing the flexibility needed to withdraw into the shell easily. The anterior dorsal region of the carapace remains well calcified and is termed the shield (Forest et al. 2000). A diagnostic character of diogenid hermit crabs is a ‘v’-shaped cervical groove of the shield (Tudge 1995). Where the carapace of a malacostracan protrudes anteriorly it is termed the rostrum (Ruppert et al. 2004). This is most obvious in shrimps, prawns and lobsters but is very reduced in most hermit crabs, including Dardanus megistos. The hermits of Diogenidae, which includes Dardanus, have a short spine positioned between the eyestalks (Tudge 1995). This is part of the acron and so is not the rostrum, which is a protrusion of the carapace