Crabs 

I’ve always regarded crabs as fascinating. You’re bound to be complex when you prefer to walk sideways and can re-grow limbs. When not on someone’s dinner plate, these decapod crustaceans scuttle around underwater and across shorelines across the world. The largest crab can reach nearly 4 metres across, while the tiniest is only a few mm wide.
All ~6,700 species of crabs have two pairs of antennae, three pairs of feeding appendages, and eyes on movable stalks for a “periscope view” when buried in the sand.