The key difference between integumentary pharyngeal and septal nephridia is that integumentary nephridia occur on all segments except the first two while pharyngeal nephridia occur in the 4th, 5th, and 6th segments and septal nephridia occur between the 15th and 16th segments.
The evolution of excretory systems in organisms shows the diversity of different levels of organisms. Earthworms belong to the phylum Annelida under the invertebrate category. The excretory system in invertebrates is called nephridium, and it mainly focuses on transferring the excretory matter to nephrastome, where they can be excreted out.
CONTENTS
1. Overview and Key Difference
2. What are Integumentary Nephridia
3. What are Pharyngeal Nephridia
4. What are Septal Nephridia
5. Similarities – Integumentary Pharyngeal and Septal Nephridia
6. Integumentary vs Pharyngeal vs Septal Nephridia in Tabular Form
7. Summary – Integumentary vs Pharyngeal vs Septal Nephridia
What are Integumentary Nephridia?
Integumentary nephridia are nephridia located in each segment of the body except for the first two segments. There are about 200 – 250 integumentary nephridia per each segment lining the body wall. The integumentary nephridia are small in size. They do not contain a nephrostome and do not contain an opening towards the coelom. Hence, this type of nephridia is also known as the ‘closed type nephridia.’
Figure 01: Nephridium
The integumentary nephridium is V-shaped. It is formed from a straight lobe and a twisted loop. The lumen of the integumentary nephridium contains two ciliated canals. Integumentary nephridium opens to the outer surface of the body directly. This opening is called the nephridiopore. Thus, integumentary nephridia release excretory contents directly to the exterior. Therefore, it is also known as exonephric nephridia.
What are Pharyngeal Nephridia?
Pharyngeal nephridia are nephridia situated in the 4th, 5th, and 6th segments of the alimentary canal. It is placed on either side and arranged as three paired tufts. Pharyngeal nephridia are similar in size to that of septal nephridia. They do not contain a nephrostome and have ciliated canals in the lumen. The structure of a pharyngeal nephridium consists of two ducts that open to the buccal cavity and pharynx, respectively. They also belong to a group of closed nephridia. The pharyngeal nephridia excrete the waste into the alimentary canal; therefore, it is also known as enteronephric nephridia.
What are Septal Nephridia?
Septal nephridia refer to nephridia situated between the 15th and the 16th segments of the body. They are placed on the posterior side of the body. Since this type of nephridia is situated in front and behind the septum, they are called septal nephridia. There are about 40 – 50 nephridia in the 15th segment. The typical septal nephridium consists of a nephrostome, neck, the nephridium body, and the terminal duct. A nephrostome is the elliptical mouth-like opening leading into an intracellular canal of the large central cell.
What are the Similarities Between Integumentary Pharyngeal and Septal Nephridia?
- Integumentary, pharyngeal, and septal nephridia are found in earthworms.
- They are the main excretory structures present in earthworms
- The nephridia are located in different segments of the body of the earthworm.
- The nephridia excrete waste in the form of urine.
What is the Difference Between Integumentary Pharyngeal and Septal Nephridia?
The key difference between integumentary pharyngeal and septal nephridia depends on their position spanning across different segments of the body. Integumentary nephridia occur on all segments except the first two, while pharyngeal nephridia occur in the 4th, 5th, and 6th segments, and septal nephridia occur between the 15th and 16th segments. Moreover, based on the presence of nephrostome, the three types of nephridia in earthworms differ. The nephrostome is only present in the septal nephridia and not in integumentary or pharyngeal nephridia.
The below infographic presents the differences between integumentary pharyngeal and septal nephridia in tabular form for side by side comparison.
Summary – Integumentary vs Pharyngeal vs Septal Nephridia
Earthworms belong to the phylum Annelida. They have a special excretory system composed of nephridia. There are numerous nephridia present in each segment of the body. Integumentary nephridia are present in all segments except the first two segments. Pharyngeal nephridia are present in the 4th, 5th, and 6th segments of the body. Septal nephridia are present between the 15th and 16th segments of the body. Moreover, only septal nephridia consist of a nephrostome while the other two types do not possess. So, this summarizes the difference between integumentary pharyngeal and septal nephridia.
Reference:
1. Baeumler, Natalie, et al. “Development of the Excretory System in a Polyplacophoran Mollusc: Stages in Metanephridial System Development.” Frontiers in Zoology, BioMed Central, 14 Sept. 2012.
2. T;, Kremer P; Fiege D; Wehe. “Morphology and Ultrastructure of the Nephridial System of HypaniaInvalida (Grube, 1860) (Annelida, Polychaeta, Ampharetidae).” Journal of Morphology, U.S. National Library of Medicine.
Image Courtesy:
1. “Metanephridium” By KDS4444 – Own work (CC BY-SA 4.0) via Commons Wikimedia