The largest water arthropod is the Japanese Spider Crab. If fully grown, it can reach a leg span of almost 13 feet, a body size of up to 15 inches and a weight of up to 20 kg. It's natural habitat is on the bottom of the Pacific Ocean, some 300 to 400 m deep, around Japan. It feeds on deed animals and shellfish. It is believed to have a life expectancy of up to 100 years.
On the other hand, the largest land-living arthropod in the world is the Coconut Crab, also known as the Birgus latro.The coconut crab derives its name from ability to crack coconuts with help of its strong pincers.Reports about the size of this crab vary, but most references give a body length of up to 16 in, a weight of up to 4.1 kg, and a leg span of of more than 3 ft, with males generally being larger than females. It is believed that this is near the theoretical limit for a terrestrial arthropod. They can live more than 30 years. This crab is eaten by the pacific islanders, and is considered a delicacy and an aphrodisiac, with a taste similar to lobster and crab meat.