Simply put, and arthropod is an animal with no backbone that has an exoskeleton with a segmented body and jointed appendages. Creatures in this phylum include insects, arachnids, and crustaceans. Surprisingly, arthropods make up about 80% of all known living species on earth. Membership includes marine, freshwater, air, and land ecosystems, being one of two major animal groups that are capable of surviving in dry land. Most arthropods are made up of three segments of the body, starting from head to "toe": head, thorax, and abdomen.