Excretory System in Earthworms

Excretory System in Earthworms

• Earthworms have specialized, coiled tubes called nephridia for excretion.
• Nephridia are found in all segments except the first three.
• There are three types of nephridia: septal, pharyngeal, and integumentary.

Septal Nephridia

• Located on the septa (the walls between segments).
• Each septum typically has 40-50 nephridia.
• Approximately 80-100 septal nephridia are present in each segment.
• It comprises a nephrostome (a wide ciliated funnel), a body, and a terminal duct.
• The nephrostome opens into the coelom.
• The body has two parts: a short, straight lobe and a long, spirally twisted loop with proximal and distal limbs.
• Ciliated canals within the nephridia, which are four in the straight lobe, one in the neck, three in the lower, and two in the upper parts of the twisted loop.
• Terminal ducts from each nephridium connect to a septal excretory canal for further processing.
• The septal excretory canal runs parallel to the commissural vessel.
• The supra-excretory canal in each segment, which is connected to the alimentary canal, receives contents from the excretory canal. Excretory products enter the alimentary canal via ducts.

Pharyngeal Nephridia

• Found in segments 4, 5, and 6.
• These nephridia lack a nephrostome.
• Terminal limbs of each nephridia of a given group join to form a common duct.
• Each segment has a pair of thick-walled ducts.
• The ducts in segments 6 connect to the buccal cavity, while ducts in segments 5 and 4 connect to the pharynx.

Integumentary Nephridia

• Similar to septal nephridia, but lacking a nephrostome.

• Shaped like a small V with a short straight and a twisted loop.

• Attached to the body wall between segments to the last.

• Each nephridium directly opens via a nephridiopore to the outside.

• The number of nephridia increases significantly (2000-2500) in the clitellar region. Often referred to as forests of integumentary nephridia.

• Septal and pharyngeal nephridia are enteronephric, excreting their contents into the alimentary canal.

• Integumentary nephridia are exonephric, excreting directly to the outside of the animal.

• Glandular cells in nephridia filter water and nitrogenous wastes (urea, ammonia, amino acids).

• These wastes are collected in the excretory canals.

• Water is reabsorbed within the alimentary canal before waste is expelled via the faeces.

Test your knowledge on the excretory system of earthworms, focusing on the structure and function of nephridia. This quiz covers the different types of nephridia and their roles in excretion.