P. crassipes is a relatively large species of intertidal crab.  The carapace is roughly 47.8 mm in fully-grown males and 40.8 mm in females, in which the head and thorax are fused together forming majority of the body called the CEPHALOTHORAX.  On front edges of the cephalothorax extends 2 black eyestalks, which are separated medially by 2 pairs of antennae.  On the underside exists 3 pairs of inner mouthparts, the mandibles and the 1st and 2nd pairs of maxillae.  

 

All brachyurans possess 8 pairs of thoracic appendages, which extend from the carapace near the gill chamber.  The first three are the outer mouthparts, 3 pairs of maxilipeds.  The fourth set of limbs is a pair of pincer-like claws, known as chelipeds.  The last 4 pairs of appendages are walking legs called pereopods. 

 

The abdomen of the crab is folded underneath the body.  On the inner abdomen, female  crabs possess 4 pairs of pleopods which carry eggs for reproduction, and males have two pairs which serve as copulatory organs.