Firstly, happy New year guys!. On today's #celestialchallenge created by 
Source
"Animal" is derived from a Latin word "Animalis" which means having soul, having life or having breathe. The kingdom "Animalia" is a classification of Eukaryotic, Multicellular organisms that exhibit Locomotion, Respiration, Nutrition, Irritation, Growth, Excretion, Reproduction, Adaptation etc. Their cells do not contain cell wall or Chlorophyll but possess cell membrane and they cannot manufacture their own food (Holozoic or Heterotrophic Nutrition).
Source
The classification of animals is called taxonomy and it is done either using the hierarchical Linnean system or the cladistics system. Aristotle first seperated plants from animals and was followed by Carl Linnaeus(a Swedish botanist) in 1735 who created the first hierarchical classification that separated the animal kingdom into class of Vermes, insecta, amphibian, aves, mammals, pisces and was thus called the father of modern taxonomy.
Source
In 1874 Ernst Haeckel further divided the animal kingdom into two sub kingdoms which were: metazoa (multicellular) and protozoa (single celled)
Animals can be classified using body structure into 2 groups which are vertebrates and invertebrates. Vertebrates are animals with backbone invertebrates are animal without backbone. Presently there are approximately 66k vertebrates and 1.3 million invertebrates species.
The divisions and subdivisions of animals are based on several important features like body symmetry, body design and body cavity
