Coelom

The coelom is a body cavity filled with fluid that is found in animals and is located between the intestinal canal and the body wall. It forms from the three germinal layers during embryonic development. The inner layer of the coelom is lined by the mesodermal epithelium cells. Animals are classified based on the presence or absence of coelom and there’s another class of animals that have a pseudo coelom. Subsequently, the animals that possess true coelom are called coelomates and those who do not have the body cavity or coelom are called acoelomates.

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Classification Based on Coelom

There are three such categories divided on the basis of the presence or absence of coelom. They are acoelomate, pseudocoelomate and coelomate.

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Acoelomate

These animals have no body cavity at all. Mesodermal tissues that are semi-solid hold the organs loosely in the blastocoel.

Example - Flatworms, poriferans like sponges, etc.

Pseudocoelomate

These animals do have a true cavity or coelom. Hence, they are called pseudocoelomates. They have a false body cavity filled with fluid. Moreover, mesodermal cells partly line the blastocoel in these animals. The mesodermal layer is found only toward the body and not near the gut. These organisms also have organs held in place loosely and they are not in an organised fashion.

Example - Roundworms, belonging to protostomes. Also, not all protostomes may be pseudocoelomates but all pseudocoelomates are protostomes.

Eucoelomate

They are also known as coelomates or organisms with the true body cavity- coelom. Their coelom has a complete mesodermal lining on both sides. Thus, the mesodermal layer is present on the body wall as well as in the gut. This lining is called the peritoneum and it allows the organs to remain attached to each other so that they can be suspended in a particular order (in an organised manner) while still being able to move freely within the cavity. During the stages of development, the blastocoel in the gastrula gets replaced by the true coelom. Example - Annelida, Chordata, Arthropoda, etc.

Types of Coelomates

On the basis of embryonic development, Coelomates are further differentiated into Protostomes and Deuterostomes. In protostomes and deuterostomes, the process of coelom development is distinct. On the basis of formation, the coelom is divided into two types: Schizocoelom and Enterocoelom. Protostomes develop Schizocoelom and Deuterostomes develop Enterocoelom.

• Protostomes: The establishment of the organism's mouth at the blastopore before its anus during embryonic development is considered to distinguish protostomes from other animals. Nematodes, arthropods, flatworms, annelids, and molluscs are well-known protostomes. Schizocoelomates is another name for them.

• Deuterostomes: The word "deuterostome" means "second mouth." Deuterostomes are animals commonly defined by their anus the anus develops at the site of the blastopore before their mouth during embryonic development. Vertebrates, including humans, sea stars, and crinoids are examples of deuterostomes.

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Schizocoelom

In these organisms, the coelom originates from the splitting of the mesoderm. It is found in annelids, arthropods, and molluscs. One part of the mesoderm attaches to the ectoderm and the other surrounds the endoderm. And the space between the two develops into a coelom. Coeloms of arthropods and Mollusca are filled with blood and are called hemocoels.

Enterocoelom

The coelom forms by the fusion of internal outgrowths of the archenteron. It pinches off and fuses and is lined by a mesodermal layer. Echinodermata and Chordates fall in this category.

Functions of Coelom

• Coelom acts as a protective layer that absorbs shocks. It absorbs most of the mechanical shocks. This cavity also provides flexibility to the organs to move. It also gives cushioning effects to the internal organs from damage on minor bends.

• The coelomic fluid is a hydrostatic skeleton that helps in locomotion for soft-bodied animals. It also gives the body a definite shape. Contracting muscles can push against the coelomic fluid as a result of the fluid pressure.

• The cells of the coelom called coelomocyte cells either float freely in the coelom or remain attached to the wall. The function of these cells is to support the immune system. They initiate the humoral immune response and phagocytosis.

• Another function of the coelomic fluid is transporting gases, nutrients, and waste products.

• Coelom provides extra space for the organs to develop properly and carry out their functions. Coelom makes the pumping of the heart possible, and also makes room for the baby in the womb.

In this article we explained what coelom is. Also, we have provided you its types and classification. To read more such topics, visit our website.