Phylum: Arthropoda

• 'Jointed appendages/legs'
• Includes insects, spiders, crustaceans, centipedes and millipedes
• Had exoskeleton consisting of chitin and protein, which is secreted by the epidermis
• In crustaceans the exoskeleton is hardened even more with calcium carbonate
• Segmentation is evident in the animals of this phylum
• Similar segments occurs in more primitive forms
• As body plan becomes more complex, number of segments decreases and becomes more specialised (different structures, different functions)
• In some arthropods some of the segments are fused together to form specialised body sections
• Insects consist of three body regions: head, thorax and abdomem
• Spiders have a fused head and thorax that forms a cephalothorax (combined head and thorax region)
• An arthropod's body has appendages with movable joints- hence the name 'jointed appendages'
• Jointed appendages enable Arthropods to move quickly and efficiently
• Bilateral symmetry and cephalisation
• Arthropods have one pair of compound eyes of a few pairs of simple eyes and antennae
• Triploblastic and coelomate
• Coelom is reduced and does not play a role as a hydrostatic skeleton because Arthropods have an exoskeleton
• coelom is a blood filled space, the haemocoel
• Blood occurs in blood vessels, but is not restricted to blood vessels, therefore is it an open blood system
• Internal organs are found in the hemocoel
• Similar nervous system to Annelida
• Specialised gaseous exchange organs. e.g tracheae in insects, gills in crustaceans and booklungs in spiders