Like all malacostracan crustaceans, the body of a hermit crab consists of twenty-one somites, or segments (Ruppert et al. 2004). This count includes the acron; the preoral, anterior-most segment, and the telson or tail segment, neither of which are considered true somites due to different embryological origins and the lack of carried appendages (Forest et al. 2000). This arrangement is comprised of five cephalic or head somites (in addition to the acron), eight thoracic somites and six abdominal somites before the telson (Ruppert et al. 2004). In malacostracans the five cephalic somites have fused with the three most anterior thoracic somites to form the cephalothorax (Forest et al. 2000). This fusion of segments is called tagmosis and the cephalothorax is then considered a tagma (Ruppert et al. 2004). The entire thorax of malacostracans is known as the pereon and the abdomen is referred to as the pleon (Ruppert et al. 2004).