Hydra captures small crustaceans by means of tentacles. Hydra is a freshwater cnidarian that feeds on small aquatic organisms, such as crustaceans, by using its tentacles. These tentacles are armed with specialized stinging cells called nematocysts, which can immobilize and capture prey. Once the prey is immobilized, the tentacles bring it to the mouth of the Hydra, where it is engulfed and digested.