Question

Protonephridia are present in Platyhelminthes and metanephridia in
(a) Annelids
(b) Arthropoda
(c) Nematodes
(d) Both (a) and (b)

Answer 1

Hint: Protonephridia is a network of dead-end tubules without internal openings, present in the phylum Platyhelminthes, Nemertea, Rotifera, and Chordata (lancelets). A metanephridium is a sort of excretory gland with a ciliated funnel opening amidst the body cavity. It is present in many invertebrates such as Annelids, Arthropods, and Mollusca.

Complete step by step answer:
Protonephridia are present in Platyhelminthes and metanephridia in Annelids and Arthropoda.
Difference between Protonephridia and Metanephridia:

Protonephridia	Metanephridia
- It refers to the tubular, excretory structures in specific invertebrates, generally closing internally in the flame cells and possessing an external pore.	- It refers to the primitive excretory organs existing in many invertebrates, arising in a ciliated coelomic funnel.
- It occurs in both coelomates as well as in Acoelomates.	- It occurs only in coelomates.
- Flame cells are present in the protonephridia.	- Nephrostomes are present in the metanephridia.
- Presence of flagellated cells in solenocytes.	- Flagellated cells are absent.
- Selective reabsorption does not take place in protonephridia.	- Selective reabsorption takes place in metanephridia.
- These are cup- shaped cells.	- These are funnel- like structures.
- Internal opening is not present whereas perforations are present.	- Internal opening is present whereas perforations are absent in metanephridia.

So, the correct answer is ‘both (a) and (b) ’.

Additional information: Similarities between Protonephridia and Metanephridia:
- Both occur in bilaterians.
- They occur in pairs.
- They are morphologically analogous to the kidneys of vertebrates.
- The main function of nephridia is to remove metabolic waste.
- They initially filter and subsequently modify body fluids.

Note: The nephridium is an invertebrate organ, found in pairs and performing function analogous to the vertebrate kidney. Nephridia remove metabolic wastes from an animal’s body. It typically had absorptive walls and ciliated or flagellated cells.