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Department Of Zoology Dr. Saheel Ahmad Class ist Year Filter Feeding in Polychaetes:The phylum Annelida is divided into four main classes and one among them is class polychaeta. Many sedentary and tubecolous polychaetes (e.g. Sabella) are filter feeders. In polychaetes, head is provided with a long bipinnate filaments or tentacles called as radides, with a ciliated groove running along their oral surface. These are used for collecting food particles suspended in water. Filter feeding means the food which is suspended in water is strained or filtered from water and eaten, the process is known as filter feeding. e.g. Chaetopterus, who lives in U-shaped tube shows filter feeding. Notopodia of segments 14-16 of this animal are modified into fans. Beating of these fans produces a water current entering the tube at the anterior end and flowing out of the other end. Notopodia of 10th segment are extremely long and wing-like or aliform. Their ciliated glandular epithelium secretes a sheet of mucus forming a bag in which the suspended food particles are caught. Mucus bags ends in a ciliated food cups where the food is rolled up into a ball. It is passed forward along a mid-dorsal ciliary groove to the mouth. Water Current in out W water current Eater in tube Along with Tube suspended food Notapodia modified in to fans animals Nephridial System In Annelida Annelida possess segmentally repeated tubes called segmental organscoelomoducts and nephridia. 1. Coelomoducts: - They are wide mesodermal tubes that develop as evagination (out pushing) from the coelom. They open at one end to the exterior by a genital pore and at the other end into the coelom by a large ciliated funnel, the coelomostome. They are confined to those segments which bear gonads as they primarily function as an exit for the gametes. Secondarily, however, the coelomoducts may take up excreatory role. 2. Nephridia: - Nephridia are segmentally arranged coiled tubes of ectodermal origin that develop as invaginations from ectoderm into coelom. They communicate with the exterior through the laterally placed small apertures called nephridiopores and internally may end blindly (protonephridia) or may open by small ciliated funnels, or nephrostomes, into coelom (metanephridia). Nephridia are primarily excreatory in function but may secondarily serve to convey the genital products to the exterior. In Polychaete excreatory organs are either protonephridia or metanephridia. (a)Protonephridia: - They are primitive type of nephridia and are found in some polychaetes e. g., Vandis they are closed internally and bear special cell. The solenocytes (or tube cells) occur singly or in groups and resemble the flame cells of Platyhelminthes and Rotifera. A solenocyte is a rather rounded ciliated cell connected to the protonephridia by a thin tube, the lumen of which encloses a flagellum. Excreatory fluid enters through the walls of Nephridial tubules which are internally ciliated. This fluid is driven into the lumen of nephridium by flagellum and forced to the exterior through nephridiopore. (b)Metanephridia: - The nephridia which open into the coelom are known as metanephridia. They are of advanced type and are found in many polychaetes, all oligochaetes and majority of leeches. Instead of solenocytes, the inner end of metanephridium opens into coelom by a ciliated funnel or nephrostome. The other end opens to the exterior through the nephridiopore. In some oligochates the nephrostomes have been secondarily lost. This condition is seen in integumentary nephridia. Principle nitrogenous waste in polychates is ammonia. Excreatory waste diffuse from coelomic fluid or blood into the lumen of nephridial tubule and discharged to outside through nephridipore. (i) Micro and Meganephridia. On the basis of their size and number, nephridia may be micronephridia or meganephridia. Micronephridia or meronephridia or smaller in size and are numerous in each segment (Pheretima). Meganephridia or holonephridia are larger in size and generally or pair per segment. They usually extend over two segments and their nephrostomes open into the segments, next infront. (ii) Exo and Enteronephridia. Nephridia are termed exonephric or ectonephric when they directly open to the exterior through nephridiopores (e. g, meganephridia of Neries, and integumentary micronephridia of Pheretima). They are termed as enteronephric when they lack nephridiopores and open into the excreatory cannals or elemantry cannal, as septal and pharyngeal nephridia of Pheretima. 3. Nephromixia:- in some Polychaeta, coelomoducts do not remain independent but become fused, parcially or wholly with the nephridia forming compound segemental organs or nephromixia. They consist both of ectoderm and mesoderm and used both as genital as well as excreatory duct. Nephridia and the coelomoducts show various degrees of combination as under:(a) Protonephromixium: - coelomoduct is united with a protonephridium. It conveys both reproductory and excreatory products to the exterior e. g, Phyllodoce. (b)Metanephromixium: - It is formed by the union of a coelomoduct with an open metanephridium e.g. Hesione. (c)Myxonephrium or mixonephridium: -It is formed by an intimate combination of coelomoduct and a nephridium, resulting in a single composite organ. The coelomoduct forms the funnel of this organ and the nephridium, its duct e. g. Arenicola. (d)Ciliated organ: - In some forms coelomoducts are reduced to ciliated organs. In Neries, they are attachged to the dorso-lateral longitudinal muscles and are known to open externally.