Blind Sac Body Plan

In the blind sac body plan, the body is essentially a sac with only one opening to the outside. Digestion takes place inside this single cavity, and both the intake of food (ingestion) and the removal of undigested waste (egestion) occur through the same opening. This plan is seen in Phylum Cnidaria, and — with variations — in Ctenophora and the free-living members of Platyhelminthes. In Cnidarians such as Hydra, this single cavity is also called the gastrovascular cavity or coelenteron because it serves both circulation and digestion, an …