Phylum annelida- excretion in annelida
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PHYLUM ANNELIDA by Priyanka Mangotra
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ABOUT ANNELIDS
• Defining charac.- one or more pairs of chitinous setae
• Complete digestive tract• Closed circulatory system• Ventral nervous system• Segmented wormsFor eg: earthworms, leeches, tubifex worms
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EXCRETORY SYSTEM OF ANNELIDS
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• Fundamental unit of excretory sys.- NEPHRIDIA
• Two pairs of nephridia in each body segment• Excrete water, mineral, salts and nitrogenous
wastes in the form of urea
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SEGMENTAL ORGANS
• There are certain tubes called SEGMENTAL organs, as they are repeated in successive segments.
• Severe to convey the excretory/reproductive products from coelom to the exterior
• They are divided into: NEPHRIDIA(derived from ectoderm) & COELOMODUCTS(from mesoderm)
• Goodrich after careful embryological study revealed that neph and coel were 2 morphologically diffrnt structures.
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COELOMODUCTS
• Segmentally arranged wide tubes of mesodermal origin
• Opens on one hand to the exterior by a genital pore & on the other into the coelom by relatively large ciliated funnel, the COELOMOSTOME.
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FUNCTIONS OF COELOMODUCTS I. Primarily as gonoductsII. Secondarily as excretory organsIII. As reproductive funnels & ducts in
oligochaeta (earthworms)IV. As the uriniferous tubules forming the
vertebrate kidney.
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NEPHRIDIA
• Segmentally arranged coiled tubules of ectodermal origin
• Ciliated internally & develped as inpushings/invaginations from the ectoderm so that they project into the coelom.
• Communicate on one hand with exterior through laterally placed small apertures called NEPHRIDIOPORES.
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Nephridium
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FUNCTIONS OF NEPHRIDIA1. Primarily function as excretory.2. Secondarily to convey the genital products to
the exterior3. May as well play some role in maintaining
salt & water balance.
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Nephridiapore Nephrostome
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TYPES OF NEPHRIDIA
• Protonephridia(closed)• Metanephridia(opened)• Mega and micronephridia• Exo and enteronephridia
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Protonephridia
• Closed type- seems to be more primitive type• Terminates in the coelom as a blind tube• Closed pre-septal end provided with peculiar
specialized excretory TUBE CELLS / SOLENOCYTES.
• Found in Vanadis, Phyllodoce, Tomopteris, etc.
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METANEPHRIDIA
• Opened type- far advanced• Absence of solenocytes, its inner pre-septal end
opens into coelom by a ciliated funnel called NEPHROSTOME.
• Thus open at both ends• Exc. Wastes diffuse from coelomic fluid/ blood into
the lumen of the nephridial tubule & discharged to the outside through NEPHRIDIOPORE.
• Found in- polychaeta(Neanthes), oligochatea (Lumbricus) & leeches
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Metanephridia
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MICRO & MEGA NEPHRIDIA
Micro/ mero nephridia• Smaller but numerous in
each seg. • Networks of fine tubes lying
on the body wall & septa in each segment.
• Found in- Pheretima.
Mega/ holo nephridia• Larger but generally one
pair per seg.• Usually extend over two
segments & their nephrostomes open into the segs. Next in front.
• Found in- Polychaeta & Hirudinea.
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• Its said a pair of originally meganephridia has broken up to form a large no. of micronephridia.
• In Megascolex, micro & mega neph. Exist even in same segment of worm.
• Serpula & other tubicolous worms- division of labour exists
Anterior region- mega neph.- excretory in function.
Posterior region- micro neph.- serve as gonoduct.
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EXO & ENTERO NEPHRIDIA
Exo/ecto nephridia• Directly open to the exterior• Nephridiopores present• Such as-Meganephridia of Nereis,
Hirudinaria & LumbricusIntegumentary micronephridia
of Pheretima.
Entero nephridia • Open into the excretory
canals / alimentary canals• Nephridiopores absent• Such as-Septal & pharyngeal nephridia
of Pheretima.
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NEPHROMIXIA
• Compound segmental organs.• Coelomoducts become fused partially / wholly
with nephridia to form nephromixia.• Consist of ectoderm & mesoderm- serve for
both excretion & exit of gametes.
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DEGREE OF COMBINATION
1. Protonephromixium-• coelomoduct +protonephridium • Convey both reproductive & excretory
products to the ext.• Found in- Phyllodoce
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2. Metanephromixium-• Coelomoduct + metanephridium• Found in- Hesione.
3. Mixonephridium- • Coelomoduct + nephridium• Funnel is formed by coelomoduct• Duct formed by nephridium• Occur in Arenicola.
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4. Ciliated organs-• Coelomoducts reduced to ciliated organs• In Nereis, they are attached to the dorso-
lateral longitudinal muscles & known to open externally.
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EXCRETORY SYS IN PHERETIMAacc to the position of neph In the body is distinguished into:
SEPTAL
•Nephrostome•Body of nephridium•Terminal duct•Nephridial ductPHARY
NGEAL
INTEGUMENTARORY
•10 times the usual no.•Called FORESTS of nephridia.
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PHYSIOLOGY
• Gland cells extract- excess water + urea + ammonia + creatinine –from blood.
• Septal nephridia eliminate solid part. From coelomic fluid through nephrostomes.
Integumentary neph(exonephric)- discharge wastes directly to the exterior.
Septal & pharyngeal neph- forms entero-nephric nephridial sys- discharge into the lumen of the gut
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Special enteronephric nephridial arrangement also serves for conservation of water / osmo-regulation.
SELECTIVE RESORPTION- excretory fluid discharged into pharynx moisten the food, as the faeces become compacted water is reabsorbed by intestine to be re-used by the body. Reabsorption of salts also occurs during fluid through the nephridia, this process is called S.R.
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Another means of excr.:CHLORAGOGEN CELLS
• Yellow cells called chloragogen cells.• Found in intestine & the dorsal blood vessel in
large no.• Derived from the peritoneum/coelomic
epithelium of the alimentary canal.• Take up nitrogenous waste products from the
blood capillaries of the gut & deposited as yellow granules(guanin) in their cytoplasm.
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• These cells are also concerned with-deamination of proteins-formation of ammonia-synthesis of ureaTherefore, they are as the vital intermediary in
metabolism of earthworms as the liver in vertebrates.
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