Despite the wide variety among species, forms exist with certain common features among themselves. These similarities form the basis of classification. Coelom is a key feature in classification of organisms. It is a cavity formed between the body wall and the gut wall which is lined by the mesodermal cells. Depending upon the presence or absence of coelom, animals are classified into three categories: Coelomate, Pseudocoelomate and Acoelomate.
> Coelomate: Such organisms show the presence of true coeloms. It originates from the mesoderm and is lined by epithelial cells of mesodermal origin. Example- Annelids, Mollusc, Echinoderms, Arthropods, Hemichordates and Chordates.
> Pseudocoelomate: In this group of organisms, the mesoderm appears as pouches between the ectoderm and endoderm. However, such coeloms don’t have a mesodermal origin and the cavity formed in this type is not lined by the epithelial cells. Example- Aschelminthes.
> Acoelomate: In this group of organisms, coelom is absent. The space between the body all and the digestive tract is filled with parenchymatous tissue. Example- Platyhelminthes.
Additional information:
Classification of organisms is very essential as it is helpful in the identification of living organisms and for better understanding of diversity among living organisms. It also helps in understanding the similarities and differences among individuals.
