Animals without a backbone or Spinal Column: Arthropdods are characterized by a segmental body covered by jointed external skeleton (exoskeleton), with paired jointed appendages on each segment.
Exoskeleton give animals protection from the outside enviroment and strong points for muscle attachment on the inside. All arthropod legs have joints and it is this feature which gives them their name. ATHROPODS MEANS " JOINT FOOTED" IN GREEK (ARTHROS: JOINT AND POUS: FOOT).
The phenomenon, called molting, is a characteristic festure fo the phylum when they grow up; it permits rapid growth in size and significant change in body form until the new exoskeleton, secreted by the animal, has hardened.
Arthropods are mainly terrestrial, but aquatic representatives are well known. They represent close to 90% of all animal species.
