Answer: There are certain physical and internal aspects of living organism that is used for the classification of animals.
Explanation: The characteristics that define an organism to be classified as animal are:-
- Segmentation that defines the segments on the bodies of the animals which are of different kind
- Whether the animal is in the category of chordata or non-chordata
- Presence of embryo stage and number of tissue layers that are getting formed while the organism is developing
- There are most chances of sexual reproduction.