How Many Types of Nephridia Are There?

Nephridia is the excretory organ found in the primitive group of animals. Although seen in a wide range of organisms, there are fundamental differences in nephridia that lead to a classification. The first division is into two types.

1. Protonephridia

2. Metanephridia

Protonephridia

In protonephridium, the organism's body is connected to a cell with an external opening. Sometimes this cell shows the presence of cilia or flagellum; in such cases, the cell is called a "flame bulb" or "flame cell." If the cilia are absent, then the cell is called a solenocyte.

Metanephridium

This Story also Contains

1. Protonephridia
2. Metanephridium
3. Septal Nephridia
4. Integumentary Nephridia
5. Pharyngeal Nephridia
6. Function of Nephridia
7. Examples

Here, the cilia do not open or are connected with any flame cell, but they directly open to the body. Here, the whole body tries to reabsorb the nutrients as they pass through. Depending on the location of the nephridia, usually in the earthworm, they can be again divided into

1. Septal nephridia

2. Integumentary nephridia

3. Pharyngeal nephridia

Septal Nephridia

The septal nephridia is made up of the nephrostome, neck, nephridium body, and terminal duct. The nephrostome is a ciliated funnel connected to the neck of the urinary tract. The neck is a junction between the nephrostome and the body of the nephridium. The body of the nephridium has loops made up of connective tissues. At the end is a terminal duct.

Integumentary Nephridia

This nephridium does not have a nephrostome or coelom opening. Therefore, these are usually known as closed nephridia. Here each nephridium connects to the outside through a nephridiopore on the skin's surface. These nephridia are also known as exonephric nephridia, as the body's wastes move directly into the external environment.

Pharyngeal Nephridia

This nephridium is present in three pairs. These also contain blood glands. Ciliated canals are present. These openings are connected to the buccal cavity and the pharynx region.

Function of Nephridia

The main function of nephridia is to excrete waste materials. The excreta of the organism, consisting mainly of urea, water, ammonia, creatinine, and a few other substances, can be removed from the body through this organ. This is similar to the functioning of kidneys in higher organisms. This organ is also important for maintaining osmoregulation.

Examples

Protonephridia is present in Platyhelminthes, such as flatworms and tapeworms.

Metanephridia is present in Annelida, such as earthworms.