All insects belong to the phylum Arthropoda. But unlike other arthropods—like lobsters, spiders, or millipedes—insects have three pairs of jointed legs, segmented bodies, an exoskeleton ...

They’re also one of the world’s largest arthropods, animals with no backbone, external skeletons, and multiple-jointed appendages. In this crab’s case, those appendages are its 10 legs.