Classify the following organisms based on the absence/presence of true coelom (i.e., acoelomate, pseudocoelomate, and coelomate)Spongilla, Sea anemone, Planaria, Liver fluke, Wuchereria, Ascaris, Nereis, Earthworm, Scorpion, Birds, Fishes, Horse.

Hint: Coelom refers to the body cavity present in most animals. It is the inner layer of the body that surrounds the digestive tract and other organs. Animals that have well-developed coelom are termed as coelomates. Animals that lack coelom are called acoelomates and animals that have coelom-like structure but not true coelom are called pseudocoelomates.

Complete step by step answer: The coelom is like a covering of the digestive system and other organs of the animals. It is present as a layer inside the mesothelium. Animals that have well-developed coelom are called coelomate like Nereis, Horse, Bird, Earthworm, fishes, and scorpion.
-It was characteristic of all triploblastic animals but was thought to be lost because of evolution. It was thought that the coelom got lost due to a reduction in body size so those animals were named acoelomates. Examples of acoelomates are Spongilla, Sea anemone, Liver fluke, and Planaria.
-They do not contain fluid-filled space or any membrane around their internal organs. They have no protection from external pressure forces.
-The other group of animals that have a fluid-filled body cavity between their body organs and digestive tract is called pseudocoelomates. They have an advantage over acoelomates as any pressure is absorbed by the fluid present around organs. These animals include Wuchereria and Ascaris.

Note: The coelomate functions to protect the internal organs of the animals. Thus, these are present in highly organized organisms as they have a large number of sensitive organs. It provides a hydrostatic skeleton in animals. Also, it absorbs any shock and supports the immune system.