Protonephridia
Protonephridium is an excretory tube that lacks an internal opening. It is found in Platyhelminthes, Rotifers, and some Chordates. The end of the tubule has solenocytes (flagellated) or flame cells (ciliated). They help in osmoregulation. The cilia or flagella creates an outward current, which in turn, produces a partial pressure. This partial pressure drives the waste metabolites from the animal. The final excretory fluid is passed through the nephridiopore or the external opening.
Metanephridia
Metanephridium is an excretory organ found in invertebrates like arthropods, annelids and molluscs. It has ciliated funnel structures which open into the body cavity that is attached to a duct. This structure finally opens to the invertebrate’s exterior. The excretory product obtained by filtration of blood is later modified into the urine. This modification happens due to the selective reabsorption in the cells lining the metanephridium.
Difference between Protonephridia and Metanephridia
Protonephridia |
Metanephridia |
|---|---|
| It is a tubular excretory organ seen in phyla like – Rotifera, Platyhelminthes, Nemertea and Chordata (lancets). | It is an excretory organ seen in phyla like – Arthropoda, Annelida and Mollusca. |
| They have either flame cells or solenocytes. | They do not have flame cells. |
| They have cup-shaped flame cells. | They have funnel-shaped structures that open into the body cavity or coelom. |
| They do not have many glandularized structures. | They have glandularized structures. |
Extended Reading: Excretory Products and their Elimination
Frequently Asked Questions on Difference between Protonephridia and Metanephridia
What are nephridia?
Nephridia are excretory organs seen in invertebrates. They have functions similar to that of a vertebrate kidney. It removes metabolic wastes from the invertebrate’s body. Metanephridia and Protonephridia are two basic categories of nephridia.
What are Malpighian tubules?
It is an excretory and osmoregulatory organ seen in insects. It is a slender tube extending from the posterior region of the alimentary canal. It absorbs nitrogenous waste, solutes as well as the water surrounding the hemolymph.
What is a nephridiopore?
The external opening of a nephridium is called a nephridiopore. The body fluid is filtered through the nephrostome and convoluted tubule. It finally reaches the nephridiopore for excretion. This nephridiopore is usually present on the ventral side.
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