(i) This is the largest phylum of the Kingdom Animalia
(ii) It includes the largest class called Insecta.
(iii) They are bilaterally symmetrical, segmented, triploblastic and schizocoelomate animals
(iv) Organization : organ system level.
(v) They have jointed appendages - used for locomotion,feeding and are sensory in function.
(vi) Body is covered by chitinous exoskeleton for protection and to prevent water loss, It is shed o periodically by a process called moulting or ecdysis.
(vii) The body consists of a head, thorax, and abdomen with a body cavity called haemocoel.
(viii)Respiratory organs : gills, book gills, book lungs or trachea.
(ix) Circulatory system : open type.
(x) Sensory organs like antennae, eyes (compound and simple), statocysts (organs of balance equilibrium) are present.
(xi) Excretion takes place through malpighian tubules, green glands, coxal glands, etc.
(xii) They are mostly dioecious and oviparous; fertilization is internal.
(xiii) Life history includes many larval stages followed by metamorphosis. eg. Limulus.
