Class Hydrozoa Hydra captures microcrustaceans, swallowing and digesting them in its gut. It uses two methods of digestion. Extracellular digestion also occurs. This process is initiated by hyfrolytic enzymes produced by gland cells in the gut lining. The absorbed nutrients diffuse to the outer layer of cells without the requirement of a circulatory system.
Undigested material is regurgitated through the mouth, one shortcoming of a single-ended gut.
With minor variations, this is the method of digestion and food transport found in all cnidarians. Stinging cells inject paralyzing poisons and enzymes that begin the process of digestion even before the prey is swallowed. Trigger hairs, brushed by a daphnia's antennae, fire out their darts and lashes. Note the violent response to contact shown by Daphania and the red copepods used in feeding trials. As the poisons take effect, the prey rapidly looses its ability to resist.