Podos → Legs
Von Siebold coined the term Arthropoda.
It is the largest group in an animal kingdom.
General characteristics of phylum Arthropoda:
- This is the largest phylum. The animal of this group is found in all habitats.
- They are triploblastic and bilaterally symmetrical.
- Body consist of jointed appendages or legs.
- The body is covered externally by a hard chitinous exoskeleton.It moulds periodically and replaces it by a new exoskeleton. It is called moulting.
- The body is divisible into head, thorax, and abdomen. In some head and thorax is often fused to form cephalothorax as in prawn.
- Cephalisation( A true head is present). It bears a pair of compound eyes, antenna and feeding apparatus.
- It is a haemo-coelom type.
- Locomotion takes place by paired lateral jointed appendages.
- The alimentary canal is straight and well developed. The mouth bears mouth parts for ingestion of food. Mouths part are modified for biting, chewing, sponging, piercing, siphoning.
- Respiration takes place by trachea or book lungs or gills.
- The circulatory system is open type consisting of perivisceral and pericardial sinuses. Blood vessels are present.
- Excretory organs take place by malpighan tubules, green glands or coxal glands. Voluntary muscles are present.
- The nervous system consists of a brain and double solid nerve cord like Annelida.
- Sense organs include antennae, compound eye, statocysts etc. The compound eye consists of many ommatidia to form several images.
- They are unisexual i.e. male and female sexes are separate. Fertilization is internal. They are either oviparous or ovoviviparous.
- Development is direct or indirect. In some species, parthenogenesis is seen.
It is classified into four classes on the basis of the number of a locomotory organ. Around 9 lakh species are present.
- Five pairs of walking legs.
- The body is divided into cephalothorax and abdomen.
- The body is externally covered by a chitinous cuticle.
- Head with two pairs of antennae.
- Respiration by gills.
- Example: Prawn, Crab, cyclops etc.
- Many pairs of walking legs.
- The body is divided into head and many segmented trunks.
- Head with one pair of antenna.
- Respiration by trachea.
- Example: Julus, Scolopendra.
Insecta or Hexapoda:
- Three pairs of walking legs.
- The body is divided into head, thorax, and abdomen.
- Head with one pair of antenna, compound eye and mouth parts.
- Respiration by trachea.
- Example: Periplaneta, Pieris.
- Four pairs of walking legs.
- The body is divided into persoma, mesosoma, and metasoma.
- The head is without an antenna. It bears chelicerae and pedipalpi for capturing and tearing the prey.
- Respiration by book lung and trachea.
- Example: spider, scorpion.