Practice question

Hemichordate coelom development is enterocoelous, characteristic of deuterostomes, where coelomic cavities form as outpocketings of archenteron endoderm that pinch off and expand. This yields three successive compartments: protocoel in proboscis, mesocoel in collar and metacoel in trunk, each lined by peritoneal mesothelium. Enterocoely contrasts with schizocoely seen in protostomes where mesodermal bands split, with pseudocoely lacking complete lining and acoely lacking cavity. Presence of enterocoely places hemichordates alongside echinoderms and chordates within Deuterostomia, supporting embryonic cleavage pattern as major phylogenetic criterion in animal systematics.