Arthropods are members of the phylum Arthropoda (from Greek árthron, “joint”, and pous (gen. podos), i.e. “foot” or “leg,” which together mean “jointed leg”).

Class distinctions include

• insects (grasshoppers, butterflies, beetles, ants, etc. 1,000,000 described world species),
• arachnids (spiders, scorpions, ticks, mites, etc. 65,000 described world species),
• crustaceans (crabs, lobsters, barnacles, isopods etc. 44,000 described world species),
• chilopods (centipedes. 2,800 described world species), and
• diplopods (millipedes. 10,000 described world species)

Arthropods are highly diverse. It is the largest of all animal phyla and accounts for over three quarters of all currently known living and fossil organisms. The exact number of living arthropod species is unknown since many have yet to be identified, especially those inhabiting tropical rainforests.