External Morphology

O. cordimanus belongs to the order Decapoda which includes shrimps, crayfishes and lobsters (Ruppert et al. 2004).  All decapods have in common: molting; separate sexes; a carapace that covers and fuses with thoracic segments; stalked, compound eyes; two pairs of antennae; two pairs of maxillae; a pair of mandibles; three pairs of maxillipeds and five pairs of walking legs (Ruppert et al. 2004).  The fusion of the head with the first three thoracic segments forms the cephalothorax (Ruppert et al. 2004).  Mouthparts are formed from maxillipeds, the first three pairs of thoracic appendanges (Ruppert et al. 2004).  The remaining five pairs of thoracic appendages are walking legs called pereopods (Ruppert et al. 2004).  The first pair of walking legs is modified to form chelae (Ruppert et al. 2004).  The remaining walking legs may be stenopodous or chelate as in crayfish, lobsters and most shrimps (Ruppert et al. 2004; Hickman et al. 2007). Male and female crabs from the Ocypode genus are heterochelous (Williams 1984).

The carapace extends laterally, covers the gills and is fused to all eight thoracic segments (Ruppert et al. 2004).   The five posterior thoracic segments are not fused to the cehphalothorax (Ruppert et al. 2004).