But unlike other arthropods—like lobsters, spiders, or millipedes—insects have three pairs of jointed legs, segmented bodies, an exoskeleton, one pair of antennae, and (usually) one or two ...

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.

Sea spiders don't do anything by the book, and researchers have just gotten to the bottom of how they breathe.