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#protonephridia

3 public questions tagged with this topic.

Animal Classification

Flame cells together form

Flame cells appear individually as ciliated terminal cells, yet collectively they connect via branching tubules forming protonephridial system, simplest nephridial type among bilaterians. Each protonephridium comprises closed tubule ending in flame bulb with filtration slits and opening externally via pore, contrasting with metanephridia that start with open ciliated funnel draining coelomic fluid. Ultrafiltration driven by ciliary beating creates negative pressure pulling fluid through weir. Thousands of flame cells provide osmoregulation in freshwater flatworms. Nephrons refer to vertebrate glomerulus-tubule units, Malpighian system originates from insect hindgut, thus protonephridia uniquely characterize acoelomates and some pseudocoelomates.

Ref: NCERT Class 11 Biology, Chapter 4: Protonephridia vs metanephridia classification

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Animal Classification

Excretory organs of flatworms are

Excretion in flatworms relies on protonephridial system, not metanephridia, Malpighian tubules or green glands characteristic of other phyla. Numerous terminal flame cells, each bulb-like cyrtocyte with tuft of beating cilia creating flickering appearance, drive ultrafiltration of interstitial fluid via negative pressure. Filtrate passes through branching tubules opening via nephridiopores, actively regulating water in freshwater species and eliminating nitrogenous waste mainly as ammonia through diffusion. This closed system lacks internal opening to coelom, unlike metanephridia in annelids which possess ciliated funnel called nephrostome. Protonephridia exemplify primitive excretory design consistent with acoelomate organization and absence of circulatory system.

Ref: Campbell Biology, 12th ed., Chapter 33: Invertebrates, excretion protonephridia flame cells

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