Practice question

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.