How do cnidarians digest their food?
Extracellularly in a digestive cavity.
Cnidarians have a gastrovascular cavity with one opening. They pull in food (smaller animals) with their stinging tentacles. In the cavity, enzymes break down the food. Nutrients diffuse directly to the body and waste is expelled out of the opening. Actually, the nutrients do not diffuse correctly my friend, it takes a little while.
Two characteristics of flatworms that make them different from cnidarians are that flatworms have a more advanced digestive system and they are flat so they can absorb oxygen faster. Cnidaria has their digestion in the gastrovascular cavity while flatworms have enzymes digest food outside of their bodies.
Since Hydra is part of the group of cnidarians, it is a bit more complicated than a sponge. The way that hydra digest their food is through extracellular digestion. This means that hydra actually have a special gut cavity that traps and digests food instead of having a bunch of cells do it, like a sponge. This gut cavity only has one opening and during digestion, enzymes from the cell wall are released to aid…