The liquid filled cavity between alimentary canal and body wall of multicellular triploblastic animals is known as body cavity. Generally, the body cavity that is lined by mesodermal peritoneal membrane is known as coelom. According to Hyman (1955), coelom is the hollow space between alimentary canal and body wall which is lined by mesodermal peritoneal tissues. Coelom gives the space for most of the visceral organs. Between two embryonic layers of mesoderm, coelom originates as a secondary body cavity. Haeckel first proposed the term coelom in 1972.
Coelom is also known as the perivisceral cavity that has fluid filled compartments, transversely partitioned by septa. In arthropods and mollusks, coelom is reduced or absent but it is present in the embryonic stage. Instead of coelom, they have space with blood and lymph, known as haemocoel. In these animals, the haemocoel is the primary body cavity while the coelom is the secondary body cavity.
Special Features of Coelom
Types of Coelom
There are the following three types of coelom, such as:
In this case, coelomic fluid-filled cavity is absent but the space between the body wall and the gut is filled by connective tissue, known as mesenchyme. The animals without a coelomic fluid-filled body cavity between the body wall and digestive tract are known as acoelomates and the group of animals is referred to as acoelomata.
Examples: Acoelomata Phyla include:
- Platyhelminthes and
In this case, coelom is not originated by the mesodermal epithelium. Embryologically, the pseudocoelom is developed from the blastocoel of the embryo. The pseudocoelom is also known as false coelom. The pseudocoelom is not bounded by the peritoneum. The fluid of pseudocoelom contains pseudocoelocytes which has no relation with the reproductive and excretory organs. Animals with a pseudocoelom are known as pseudocoelomates and the group of animals is referred to as pseudocoelomata. Pseudocoelomata are also referred to as blastocoelomata or haemocoelomata.
Examples: According to Brusca and Brusca (2003), pseudocoelomata phyla include:
In this case, the body cavity between the gut and body wall is bounded by peritoneum. Peritoneum is derived from the embryonic mesoderm. This type of cavity or coelom is known as eucoelom or true coelom. The coelomic fluid of true coelom contains amoebocytes. The animals with true coelom are known as coelomates and the group of animals is referred to as coelomata.
Examples: According to Brusca and Brusca(2003) the following phyla possess a true coelom:
Some Similarities Between Coelom and Pseudocoelom
Difference between Coelom and Pseudocoelom
The following table shows the differences between coelom and pseudocoelom:
Coelom is a fluid filled true body cavity, present between the body wall and the digestive tract.
Pseudocoel is a fluid-filled body cavity, present between the mesoderm and the endoderm.
Coelom is also known as eucoelom or true coelom.
Pseudocoelom is also known as false coelom.
The animals with true coelom are known as coelomates and the group of animals is referred to as coelomata.
Animals with a pseudocoel are known as pseudocoelomates and the group of animals is referred to as pseudocoelomata.
Coelom or true body cavity is lined with peritoneum.
Pseudocoelom or false body cavity is partially lined with peritoneum.
The coelom is developed by splitting of the mesoderm.
The pseudocoelom is developed from the blastocoel of the embryo.
In this case, the blood stream carries the nutrients.
In this case, the nutrient transportation occurs through osmosis and diffusion.
Pseudocoelom is present only in invertebrates.
The organs present inside the coelom are Well-organized.
The organs present inside the pseudocoelom are less-organized.
Examples: Nematoda, Entoprocta, Rotifera, Acenthocephala, and Gastrotrica, etc.
Functions/Significance of Coelom
Coelom makes the partition to separate biological systems that perform various major functions. Acoelomates transport nutrients around the body through diffusion due to relatively small with less intricate body plan. In this case, diffusion is enough to perform transport function. The coelomates have complex body plan that need special transport system (circulatory system) to ship the nutrients around the body. In this case, coelom is useful to separate circulatory system from abdominal organs.