Arthropods are a diverse group that includes anything with paired jointed legs and a hard external skeleton (including insects, arachnids, and crustaceans). Behold the humble Coconut Crab (aka Birgus latro), the world's largest terrestrial arthropod:
The coconut crab is a derived species of hermit crab, though only juveniles carry around an abdominal cover (usually a seashell or coconut husk). Adults have a typical leg span of 3 feet and weigh 9 pounds. Larger specimens have been found spanning 6 feet and weighing 30 pounds.
The coconut crab is omnivorous, though it primarily dines on fleshy fruit, nuts, and seeds. The claws are as powerful as they are large - they can lift objects such as vegetation or rocks weighing up to 60 pounds (28kg) and use their massive claws to pry open all sorts of food (hence the origin of their name). Coconut crabs live alone in underground burrows, covering the entrance to keep the high humidity necessary for their lungs to function. While usually nocturnal they do occasionally venture out during the day if it's rainy or foggy.