5 public questions tagged with this topic.
Arthropods have a hemocoel, where the body cavity is filled with blood and functions as an open circulatory system.
Ref: NCERT Class 11 Biology Chapter 4: Animal Kingdom Basis of Classification - Symmetry Coelom Segmentation
Enterocoelous formation of mesoderm and true coelom characterizes deuterostome development seen in Echinodermata Hemichordata and Chordata contrasting with schizocoelous mode in protostomes. During gastrulation archenteron wall evaginates as paired mesodermal pouches pinching off from endoderm expanding into blastocoel lumina coalescing to become eucoelom lined by mesoderm. Process termed enterocoely indicates gut origin of coelom. In echinoderms three pairs form axocoel hydrocoel somatocoel. Contrasts with schizocoelous where coelom forms by splitting mesodermal mass. Enterocoely produces trimeric organization in some deuterostomes emphasizing archenteric mesoderm source and deuterostome monophyly defined in embryology.
Ref: Campbell Biology, 12th ed., Chapter 32: Enterocoelomate coelom formation deuterostomes; NCBI
Pseudocoelomate body plan shows variation among Aschelminthes. In Nematoda body wall comprises resistant collagenous cuticle, syncytial hypodermis and only longitudinal muscle layer, circular muscle absent, enclosing fluid-filled pseudocoel at high turgor functioning as hydroskeleton. Musculature restricted to outer peripheral position muscles lie only on outer side of pseudocoel not lining gut. Contrasts with true coelomates where muscle layers border both sides of coelom. High internal pressure enables undulatory thrashing locomotion. Hence animal exhibiting pseudocoelom with muscle solely peripherally corresponds to nematode organization illustrating evolutionary intermediate between acoelomate and eucoelomate architectures and adaptation to interstitial and parasitic existence worldwide.
Ref: NCERT Class 11 Biology, Chapter 4: Pseudocoelom Nematoda muscles; Campbell Chapter 33
Despite colonial modular construction ectoprocts possess organization as true eucoelomates with compartmentalized coelomic cavities lining gut and body wall derived from mesoderm bordered by ciliated peritoneal mesothelium containing coelomocytes. Coelomic fluid functions as hydrostatic skeleton, pressure generated by contraction of parietal muscles protrudes lophophore for feeding, accommodates retractor bundles pulling polypide inside zooecium. Each autozooid possesses separate coelomic compartment though reduced due to small size. Presence aligns ectoprocts with phoronids and brachiopods as coelomate lophophorates distinguishing them from acoelomate platyhelminths or pseudocoelomate nematodes correcting former interpretation as acoelomate or diploblastic organisms historically misclassified in textbooks.
Ref: Brusca & Brusca, Chapter 23: Bryozoa coelom; Ruppert Invertebrate Zoology, Lophophorates
Coelom or true body cavity defined by complete lining of mesoderm-derived peritoneum on both outer somatic side lining body wall as parietal layer and inner splanchnic side covering visceral organs as visceral layer, with mesothelium secreting serous fluid cushioning organs and providing hydrostatic skeleton. Contrast pseudocoelom where outer wall mesodermal but gut wall endodermal not peritoneal, blastocoel persistent embryonic cavity not mesodermal, and acoelom solid mesenchyme. Annelids, arthropods secondarily modified, molluscs reduced, chordates prominent exemplify eucoelom providing compartmentalization and mesentery suspension.
Ref: Brusca & Brusca Invertebrates Coelom Definition; NCERT Class 11 Chapter 4 Body Cavity
