Phylum: Arthipoda

• Arthos- pointed &podos-legs
  They have jointed legs or appendages.

• Habitat:
  This is the largest phylum and found in all types of habitats and cosmopolitan in distribution.

• Germ layers:
  They are triploblastic having 3 germ layers.

• Symmetry:
  They are bilaterally symmetrical.

• Body Grade:
  Body contains organ system grade of organization.

• Coelom:
  They are heoemocuolomic, coelomic cavity filled with blood.

• Body division:
  Body is divided into head, thorax and abdomen. In some, head and thorax is fused to form cephalothorax (E.g. Palaemon).

• Cephalisation:
  They have distinct cephalisationisation re. Distinct head is present. Head bears compound eyes, antennas and mouth parts.

• Body covering:
  Body is covered by chitinousexo-skeleton.

• Nutrition:
  Nutrition is holozoic and some are ectoparasitic blood sucking form. (E.g. mosquito)

• Alimentary canal:
  They have well-developed, straight and complete alimentary canal.

• Digestion:
  Digestion extracellular or inter-cellular inside the alimentary canal.

• Respiration:
  Respiration occurs by trachea, booklungs, gills and spiracles.

• Circulatory system:
  It is of open type i.e. absence of blood vessels and the blood flows through body cavity.

• Excretion:
  Excretion occurs by the malphigiantubeles or coaxial glands or green glands.

• Nervous system:
  It consists of brain, ganglia, ventral double nerve cord and nerve fibres.

• Sensory Organs:
  Presence of sensory organs such as antennae, eyes, photo receptor. Audio receptors, statocysts etc.

• They are unisexual.

• Fertilization is internal.

• They are oviparous as well as viviparous (e.g. Palaemon)

• Development: Indirect and direct both are seen.
  Example: Palaemon, Araneaetc

Classification: Phylum arthopoda has been classified into 4 classes on the basis of walking legs:-

A. Insecta

1. They bear three pairs of walking legs.
2. Body possesses a pair of antennae.
3. Wing may be one pair (housefly) or absent in some (bed bug).
4. They are air breathing, mostly terrestrial and rarely aquatic forms. Some parasites on the bodies of other animals.
5. Respiration occurs by trachea with external openings in the form of spiracles. Examples Periplarenta amaricana, Bombyx etc.

B. Arachnida

1. They bear 4 pairs of walking legs.
2. Body possesses no antenna.
3. They are air breathing terrestrial arthropods. Some are parasites. They are especially abundant in the warm dry region.
4. Respiration occurs by the trachea or book lungs. Example Paramaeus, Arance etc

C. Crustacea:

1. They bear 5 pairs of walking legs.
2. Body possesses 2 pairs of antennae.
3. They are mainly aquatic, mostly marine, little water and few live in moist places on land while few are parasitic.
4. Respiration occurs by gills, epipodites &branchiostegibes.
5. The body is covered externally by chitinous cuticle. Example Cancer, Palaemon etc

D. Myriapoda:

1. They bear many legs i.e. they are multi-legged.
2. Body possesses a pair of antennae.
3. They are terrestrial, found under legs of wood, stones etc.
4. They respire through trachea.
5. They are fast running arthropods. Example Julus, Scolopendra etc