- Phylum Arthropoda is the largest phylum of Animalia which includes insects.
- They have organ-system level of organization, they are bilaterally symmetrical, triploblastic, segmented and coelomate animals.
- The body is covered by chitinous exoskeleton.
- The body consists of head, thorax and abdomen and have jointed appendages.
- Respiratory organs are gills, book gills, book lungs or tracheal system.
- Circulatory system is of open type, sensory organs like antennae, eyes, statocysts are present, and excretion takes place through Malpighian tubules.
- They are mostly dioecious, fertilization is internal, mostly oviparous, and development may be direct or indirect.
Economically important insects – Apis (Honey bee), Bombyx (Silkworm).
Vectors – Anopheles, Culex mosquito.
Living fossil – Limulus (King crab).
Gregarious pest – Locusta (Locust)