What cells in a hydra serve as a means of attack or defense?

The freshwater hydra hunts and defends itself using special cages, most of which are located on the tentacles. They got the name from the mechanism of action – stinging cells. They are located in the ectoderm, such cells contain a container with a twisted thread, outside there is a special process, when irritated, a signal is sent to the cell and the thread is thrown out, hitting prey or the enemy. A substance with a paralyzing effect passes through the channel of the thread. Stinging cells are divided into three types, depending on the principle of the thread. It can act as a harpoon, piercing the integument, or wrap around the body of the prey, and the third option is that they stick to the body of the prey due to the sticky substance in which the thread is lubricated.