What reason are cnidoblasts important to the hydra?

A genus of small, freshwater cnidarians (coelenterates) which belong to the class Hydrozoa. Hydra is an exceptional member of this class because it is a mobile individual polyp rather than a sessile or colonial form, and uses its cnidoblasts to capture prey. Unlike most Hydrozoa, which spend at least part of their lives in a medusa form, which reproduces sexually, Hydra exists only as polyps. They are typically a few millimeters long.