13 public questions tagged with this topic.
Flame cells are the excretory structures in Platyhelminthes, helping in osmoregulation.
Ref: NCERT Class 11 Biology Chapter 16: Excretory Products and their Elimination Nephron Structure - Glomerulus and Bowmans Capsule
Planaria (a platyhelminth) uses flame cells for osmoregulation and excretion.
Ref: NCERT Class 11 Biology Chapter 4: Animal Kingdom Phylum Ctenophora and Platyhelminthes
Platyhelminthes use flame cells for excretion and osmoregulation.
Ref: NCERT Class 11 Biology Chapter 4: Animal Kingdom Phylum Ctenophora and Platyhelminthes
Flame cells in platyhelminthes help in excretion and osmoregulation.
Ref: NCERT Class 11 Biology Chapter 4: Animal Kingdom Phylum Ctenophora and Platyhelminthes
Platyhelminthes (flatworms) are triploblastic, acoelomate, and bilaterally symmetrical, but they lack a circulatory system.
Ref: NCERT Class 11 Biology Chapter 4: Animal Kingdom Basis of Classification - Symmetry Coelom Segmentation
Platyhelminthes have an incomplete digestive system, meaning they have only one opening for ingestion and egestion.
Ref: NCERT Class 11 Biology Chapter 4: Animal Kingdom Basis of Classification - Symmetry Coelom Segmentation
Platyhelminthes are triploblastic and acoelomate, meaning they lack a true body cavity.
Ref: NCERT Class 11 Biology Chapter 4: Animal Kingdom Basis of Classification - Symmetry Coelom Segmentation
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
Flatworm digestive tract remains incomplete, possessing single ventral or anterior mouth opening into blind gastrovascular cavity lacking anus, distinguishing from complete tube. Food enters same orifice, digestion proceeds extracellularly in lumen and intracellularly within gastrodermal cells, undigested residues egested through mouth. Cavity may be sac-like in Acoela, bifurcated in triclad planarians or extensively branched in polyclads increasing absorptive surface area. Parasitic cestodes secondarily lost gut entirely absorbing nutrients across tegument via facilitated transport. Evolution of complete through-gut with separate anal opening in nematodes and higher phyla improves directional processing, regional enzyme specialization and continuous feeding unavailable to Platyhelminthes.
Ref: NCERT Class 11 Biology, Chapter 4: Animal Kingdom, Platyhelminthes incomplete gut
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
Digestive system with single opening functioning as both mouth and anus termed incomplete gut or blind sac. Cnidarians exhibit gastrovascular cavity where food enters through mouth surrounded by tentacles extracellular digestion begins absorption primarily intracellular via phagocytosis residues expelled same aperture. Similar condition seen in Platyhelminthes with branched gut increasing area. Complete gut with two separate openings enables unidirectional transit regional specialization continuous feeding larger body size innovation arising in Nematoda onward. Incomplete gut correlates with radial symmetry relatively low metabolic demands limiting efficient throughput and complexity in diploblastic grade animals with tissue organization and extracellular digestion.
Ref: NCERT Class 11 Biology, Chapter 4: Incomplete gut cnidarians gastrovascular; Campbell Biology
Nemerteans superficially resemble turbellarian flatworms due to dorsoventrally flattened ciliated creeping body, soft unsegmented appearance, but fundamentally distinguished by several evolutionary advances: possession of true complete tubular system with separate anterior mouth and posterior anus allowing continuous unidirectional processing and fecal egestion, compared to incomplete blind branching gastrovascular cavity of Platyhelminthes, plus development of well-organized closed circulatory system with dorsal ventral vessels containing nucleated erythrocytes with hemoglobin absent in flatworms. Additionally possess protonephridial excretory system and unique rhynchocoel containing proboscis elevating them to higher grade approaching coelomates.
Ref: Ruppert et al., Invertebrate Zoology, Chapter 20: Nemertea complete gut closed circulation
