The basic body plan of a horseshoe crab consists of three parts: the prosoma, the opisthosoma and the tail (telson). The prosoma is the large, dome-shaped frontal part at the carapace. The smaller rear carapace with spines on the edge is the opisthosoma. The rear extension that looks like a spike is the telson, which is commonly described as the tail. Uniquely among the horseshoe crabs, the cross section of the tail of the mangrove horseshoe crab is rounded. It is essentially triangular in the other species. The tail is used to turn itself right side up when overturned.