Coelom

A body cavity is any space, compartment, or potential space within an animal's body. The Coelom is a fluid-filled cavity that houses and supports organs. It is located between the body wall and the gut wall and is lined with mesodermal tissue. 

1.0Animals Based Upon Types of Coelom

Acoelomates

• The Acoelomates are relatively simple triploblastic animals with no perivisceral body cavity or Coelom. 
• The space between the digestive tract and the body wall is filled with parenchyma, a tissue derived from the mesoderm. 
• Example - Flatworms.

Pseudocoelomates

• Pseudocoelomates are a group of invertebrates characterized by having a hollowed body cavity called a pseudocoelom. 
• This pseudocoelom is a fluid-filled space located between the outer body wall (derived from ectoderm) and the digestive tube (derived from endoderm). 
• Mesoderm is present but does not make the lining of the body cavity. 
• Example - Nematodes (Roundworms) and Rotifers

Eucoelomates

• Animals that possess a true coelom are referred to as eucoelomates or coelomates. 
• This type of body cavity is situated between the digestive tract and the body wall is completely lined with mesothelium.
• Examples of eucoelomates include earthworms, snails, insects, starfish, and vertebrates.

Types of Eucoelom

Schizocoelom:

• Schizocoelom is present in protostomes. 
• The body cavity originates from the splitting of mesoderm. One part attaches to the ectoderm, and the other surrounds the endoderm. 
• The space that develops between these tissues becomes the Coelom. In this process, the blastopore evolves into the mouth. The Coelom itself forms from mesodermal blocks surrounding the gut, which expand and create a hollow cavity. 
• Examples of animals with this type of Coelom include Annelida (segmented worms), Mollusca (mollusks), and Arthropoda (arthropods).

Enterocoelem:

• Enterocoelom develops from the embryonic gut or endoderm pocketing. 
• In this type, the body cavity is formed by a primitive gut that breaks off and forms the Coelom. It is present in the deuterostomes. 
• The Coelom is developed from the fusion of the archenteron's internal outgrowths, which pinch off and fuse to form a coelom lined by mesoderm. 
• Examples-Echinodermata and Chordata

2.0Structure of Coelom

3.0Protostomes and Deuterostomes

Bilaterally symmetrical, triploblastic eucoelomates can be categorized into two groups based on differences in their early embryonic development.

They are, 

1. Protostomes

2. Deuterostomes 

Protostomes:

• The word protostome comes from Greek words meaning "mouth first". The opening of the digestive cavity or Coelom first develops in the mouth. 
• Examples-Arthropods, Molluscs and Annelids. 

Deuterostomes:

• Deuterostome originates from words meaning "mouth second". In this, the opening of the digestive cavity or Coelom develops, the anus develops first. 
• This distinction is based on the fate of a structure known as the blastopore. Protostomes and deuterostomes differ in several developmental aspects, such as the method by which the coelom forms and the pattern of early cell division in the embryo. 
• For example, chordates and echinoderms represent these two major groups.

4.0The Importance of Coelom

• The Coelom is extremely important in the lives of animals.
•  These are: 
• The coelomic fluid content facilitates the smooth transportation of particles or materials in solution. 
• Coelom functions as a shock absorber and protects against mechanical shock. Coelom affords flexibility to the body's organs to move and protects them from any damage during the bends of the internal organs. 
• Gonads, which develop from coelomic epithelium, are housed in the cavity of the Coelom. The nephridial tubules, which connect the Coelom to the exterior and, in some cases, allow the passage of eggs and sperm, are also housed in the cavity of the Coelom. 
• The Coelom is a hydrostatic skeleton filled with incompressible coelomic fluid that aids in the locomotion of soft-bodied animals and gives the body a definite shape. 
• The coelomocyte cells, which either float freely in the Coelom or are attached to the wall, support the immune system by initiating the humoral immune response and phagocytosis. 
• The coelomic fluid also helps in the gaseous transport of nutrients and waste products. 
• Coelom gives the extra space required by organs to develop and function. Because of Coelom, things like heart pumping, carrying a child in the womb, and so on are possible. 

5.0Coelomic Fluid Definition

• The fluid within the Coelom is called coelomic fluid. It is circulated through the Coelom either by the movement of cilia on the mesothelial lining or by the contraction of muscles in the body wall, which are composed of mesodermal tissue.

Significance of Coelomic Fluid

• The coelomic fluid performs several key functions:
• Hydroskeleton: It provides structural support and helps maintain the shape of the body.
• Movement and Growth: It facilitates the free movement and expansion of internal organs.
• Transport: It aids in the circulation of gasses, nutrients, and waste products throughout the body.