Re: How do hydra digest food

Hydra are members of the phylum CNIDARIA. These are the next animal "up" 
from sponges.

An evolutionary advance the Cnidarians have over sponges is extracellular 
digestion of food. What this means is Cnidarians actually have a special 
gut cavity for digestion of captured food, rather than allowing each cell 
to do it, like a sponge does. All animals from Cnidarians up have kept 
this feature! It's very important and allows the animal to be much more 
efficient.

Cnidarians (and Hydra) have a gut cavity with only a single opening. 
Digestive enzymes are released from the gut wall and help in the break-
down of the food. Once the food has been broken up into smaller particles, 
cells from the gut wall start engulfing the bits using the 
process "phagocytosis" (the same way an amoeba feeds).

The incredible thing about Cnidarian digestion is that when they arose, 
they were the first animal ever to be able to eat and successfully digest 
a piece of food LARGER that itself (although only small pieces by small 
pieces).

I hope this information is useful.

Kind regards,

Alastair