Practice question

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.