Nematocysts are small sacs with patchy filaments located in nidocyte cells. Normally the sutraka is inserted into a sac or capsule with a butt and a fork. A nematocyst once shed never reenters. In 1965, scientist Werner identified 23 types of nematocysts in the bodies of Nideria animals. However, four types of nematocysts can be seen in Hydra. Dr. Siddiq Publications
1. Stenotile or penetrant: Stenotile is the largest of the four types of nematocysts of Hydra. Its capsule is filled with a poisonous liquid called hypnotoxin. Its butt is fat. The butt has three large spines. It’s called a barb. Butt has three rows of barbules.
Work of stenotil or penetrant
(i) It paralyzes prey with hypnotoxin.
(ii) Its trigger grips the prey.
2. Streptolin Glutinant or Holotrichus isorhiza: Streptolin Glutinant medium type nematocyst. Its capsule is small and the butt is not well formed. It lacks barbs, but has barbules. Its stems are long, spiny and open at the apex.
Action of Streptolin Glutinant
(i) It traps prey.
(ii) Helps in locomotion.
(iii) secretes sticky substances.
3. Steriolin glutinant or Atrichus isorhiza: Steriolin glutinant is the smallest nematocyst. Their butt is not well formed. Barbs and barbules are absent. Its stems are short, thornless and open at the apex. Dr. Siddiq Publications
Action of stearoline glutenin
(i) It helps in locomotion.
(ii) binds the hydra to an object.
(iii) secretes sticky substances.
(iv) Capture the victim.
4. Volvent or Desmonym: Volvent is a relatively small nematocyst. They do not have butts, barbs and barbules. Its stem is thick, short, elastic, spineless and closed at the apex. There is only one patch of Sutra inside its capsule. The sutraka remains patchy even when thrown. As soon as it is thrown, it creates many screws like a cork-screw.
Volvent’s work
(i) It grasps the prey.
(ii) It helps in locomotion.