General characters of Arthropods: 1. Arthropoda is bilaterally symmetrical, triploblastic and metamerically segmented animals. 2. Body can be divided into head, thorax and abdomen; head and thorax are often fused to form cephalothorax. 3. Body is covered with a thick chitinous cuticle forming an exoskeleton. 4. Body segments usually bear paired and jointed appendages. 5. Coelom largely a blood - filled haemocoel. 6. Muscles are mostly, striated, usually capable of rapid contraction. 7. Digestive tract is complete. The mouth and anus lie at opposite ends of the body. 8. Circulatory system is open with dorsal heart and arteries and blood sinuses. 9. Respiration through by general body surface, by gills in aquatic forms, by tracheae and by book lungs. 10. Nervous system has dorsal nerve ring. 11. Excretory organs are Malpighian tubules (in insects) and green glands (in Crabs and prawn). 12. Cilia are absent from all parts of the body. 13. Sexes are generally separate. 14. Fertilization is internal, oviparous and ovoviviparous. 15. Parental care is well marked in many arthropods.