EXCRETION IN EARTHWORM for high school.pptx

Important notes

1. Excretory system Organ system concerned for the expulsion of nitrogenous wastes produced in the body due to metabolic activities. Earthworm is ureotelic as well as ammonotelic. In Pheretima, excretion is carried out by segmentally arranged, microscopic, long, thin, coiled tubes called nephridia. Nephridia occur in all segments of the body except first two. Small sized nephridia called micronephridium are found in earthworm as compared to large sized (=meganephridium) found in Leech and Nereis. According to their location in the body they are distinguished into 3 types: Pharyngeal , Integumentary and Septal nephridia .

2. Contd…. Different types of nephridia and their location in Pheretima Pharyngeal : at 4 th 5 th and 6 th segment. Integumentary : entire body wall except first two segments. Septal : from inter-segmental septum of 15/16 segment onwards. Nephridia and their location

3. Contd… A Septal nephridium

4. Contd… 1. Pharyngeal nephridia Occur as paired tufts on either side of pharynx and oesophagus in the 4 th , 5 th and 6 th segment. Each tuft consist of hundreds of coiled branched tubules without nephrostomes. In each tuft, the terminal duct of all tubules join to form a single thick-walled common duct. There are 3 pairs of common pharyngeal nephridial ducts which run anteriorly parallel to the ventral nerve cord. Ducts of 4 th and 5 th segments open into pharynx while those of 6 th segment open into buccal chamber. Pharyngeal nephridia are thus enteronephric (discharge waste to gut). Extract waste from only capillaries.

5. Contd… 2. Integumentary nephridia Distributed on the entire inner and outer surface of body wall in segments except first two. About 200-250 in all segments except cliteller segments. Clitellum (14 th ,15 th and 16 th segments) contain about 2000-2500 integumentary nephridia. Hence called “forest of nephridia”. Nephridia are microscopic, V-shaped and lack nephrostome. The terminal duct of these nephridia open exteriorly through minute openings (= nephridiopores ) on body surface. These nephridia are thus exonephric . Extract waste product only from capillaries.

6. Contd… 3. Septal nephridia Largest nephridia of earthworm with nephrostome. Found attached to both the faces of each intersegmental septum behind 15 th segment. About 80-100 nephridia on each septum. Nephridia remain suspended freely in coelom of each segment and are enteronephric. Has 3 parts: i . Nephrostome ii. Body iii. Terminal duct. i. Nephrostome ciliated funnel communicating with coelom. consist of a pore bounded by ciliated upper and lower lip. continuous movement of cilia help to absorb nitrogenous waste from coelomic fluid.

7. Contd… ii. Body Nephrostome leads into body through a short, narrow and ciliated neck. Body consist of two parts- a short straight lobe, and a long twisted lobe with a narrow apical part. Twisted lobe consist of a proximal limb and a distal limb which are spirally twisted upon each other. Proximal limb is joined to the neck. iii. Terminal duct Distal limb of body of nephridium ends into a short and narrow duct called terminal duct. Terminal ducts open into a pair of septal excretory canal which again lead to supra-intestinal excretory ducts. Supra-intestinal excretory ducts open into intestine in each segment through narrow ductules , each having sphinctered opening.

8. Contd… A:- Entire nephridium B:- L.S. of Nephrostome

9. Contd.. Arrangement of septal nephridia on a septum

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