System of classification of animals

Animals can be classified into two groups :
(a) Invertebrates ( animals without back-bones )
(b) Vertebrates ( animals with backbones )

Invertebrates

1. Invertebrates are animals which do not have backbones.
2. Invertebrates make up the most number of animals in the world.
3. Most invertebrates live in the water.
4. Some invertebrates have a hard external skeleton for protection like the crab and the beetle.
5. Some invertebrates have soft bodies using their body fluids for support like the earthworms and leeches.
6. Generally, invertebrates can be classified into two groups, that is
(a) with jointed legs
(b) without jointed legs