Coelom : The coelom is a body cavity which develops during embryonic development of an animal between ectoderm & endoderm, and it may or may not be lined by mesoderm or it may be absent in some animals. The presence absence & type of coelom is also a basic feature used in animal classification –
Acoelomate: The animals without any cavity between ectoderm and endoderm. There are mesenchyma tissues (mesodermal in origin) between ectoderm & endoderm.
Example- Platyhelminthese.
Pseudocoelomate: They have a body cavity between ectoderm and endoderm but it is not lined by the mesoderm.
Example- Aschelminthese
Eucoelomate: They have a body cavity between ectoderm and endoderm which is lined by the mesoderm. It is also c/a true coelom and its is of two types of the basis of origin
(a) Schizocoelomate: The true coelom which is formed by the splitting of the mesoderm during embryonic development. The measoderm along with ectoderm (Body wall) is called as somatic mesoderm and with endodenn (Alimentary canal) is c/a splanchnic mesoderm.
Example- Annelida, Arthropoda, Mollusca.
(b) Enterocoelomate: The true coelom which is formed as a pouch from the endodenn, similarity, the mesoderm layer with ectoderm is c/a somatopleur and with endoderm as splanchnopleur.
Example- Echinodermata. Chordata
