The Arthropods are the largest and most successful Phylum on this planet!!
All of the Insects, Spiders, Crabs, Prawns, Millipedes, Centipedes and many other groups of fascinating animals are Arthropods, all told arthropods make up more than 80% of the animal Kingdom.

An Arthropod is an animal that possesses these characteristics.
          A) a mouth and anus at opposite ends of a through gut,
          B) a hard jointed exoskeleton,
          C) jointed limbs.

The Phylum Arthropoda is divided into 5 Subphyla (4 still in existence) each of which is in turn divided into various Classes.