Describe the largest phylum of Animalia.

(N/A) $\rightarrow$ Arthropoda is the largest phylum of Animalia which includes insects.
$\rightarrow$ Over two-thirds of all named species on earth are arthropods.
$\rightarrow$ They have organ-system level of organisation.
$\rightarrow$ They are bilaterally symmetrical,triploblastic,segmented and coelomate animals.
$\rightarrow$ The body of arthropods is covered by chitinous exoskeleton.
$\rightarrow$ The body consists of head,thorax and abdomen.
$\rightarrow$ They have jointed appendages (arthros-joint,poda-appendages).
$\rightarrow$ Respiratory organs are gills,book gills,book lungs or tracheal system.
$\rightarrow$ Circulatory system is of open type.
$\rightarrow$ Sensory organs like antennae,eyes (compound and simple),statocysts or balance organs are present.
$\rightarrow$ Excretion takes place through malpighian tubules.
$\rightarrow$ They are mostly dioecious.
$\rightarrow$ Fertilisation is usually internal.
$\rightarrow$ They are mostly oviparous.
$\rightarrow$ Development may be direct or indirect.
$\rightarrow$ Examples: Economically important insects -
$\rightarrow$ Apis (Honey bee)
$\rightarrow$ Bombyx (Silkworm)
$\rightarrow$ Laccifer (Lac insect)