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Phylum – Arthropoda


This is the largest phylum of Animalia which
includes insects. Over two-thirds of all named
species on earth are arthropods (Figure 4.12).
They have organ-system level of organisation.
They are bilaterally symmetrical, triploblastic,
segmented and coelomate animals. The body
of arthropods is covered by chitinous
exoskeleton. The body consists of head, thorax
and abdomen. They have jointed appendages
(arthros-joint, poda-appendages). Respiratory
organs are gills, book gills, book lungs or
tracheal system. Circulatory system is of open
type. Sensory organs like antennae, eyes
(compound and simple), statocysts or balance
organs are present. Excretion takes place
through malpighian tubules. They are mostly
dioecious. Fertilisation is usually internal.
They are mostly oviparous. Development may
be direct or indirect.
Examples: Economically important insects –
Apis (Honey bee), Bombyx (Silkworm), Laccifer
(Lac insect)
Vectors – Anopheles, Culex and Aedes
(Mosquitoes)
Gregarious pest – Locusta (Locust)
Living fossil – Limulus (King crab).
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