What are the basic plans of body design in animals?
Animals can be classified into three basic plans: (i) Cell Aggregate Plan: - It is found in simple animals such as sponges, which have clusters of cells with the rudimentary division of labour. (ii) Blind Sacs Plan: - It is found in coelenterates and flatworms. They have a digestive cavity with only one opening to the outside world. Food is ingested and undigested waste is expelled through this opening in the mouth. The cells are more specialised and have a division of labour. (iii) Tube- within a tube plan: - It is found in more complex forms. In this plan, the body cavity forms one tube within which another tube, the alimentary canal, is located, opening on one side by the mouth and the other by the anus.
