Robber crabs belong to the Phylum Arthropoda of the invertebrates in the Kingdom Animalia.
Arthropods are invertebrates having the characteristic features like the exoskeleton which is the external skeleton made up of chitin, body plan consisting of the segmented body and paired jointed appendages or limbs. Coconut crabs or the Robber crabs also show the same characteristic features. They show a segmented body with a front portion called the cephalothorax showing ten legs and an abdomen. The adults develop a tough exoskeleton for protection. There are a pair of ten jointed appendages with each pair having a particular function. Thus, they belong to the phylum Arthropoda.