The body cavity of animals of the order Nidaria is called a coelenteron. The body cavity of the Hydra is the Cilantron. Archenteron transforms into Cilenteron. It is covered by gastrodermis. It involves extracellular digestion. Food and excreta are transported through it. Hence it is called Gastrovascular cavity. Cilantron is sometimes called blind gut or blind sac. It is exposed through the stoma. Takes food and leaves waste through mouth. Dr. Siddiq Publications
Why Coelenteron is called digestive circulation
Both alimentary canal and body cavity functions of Nidaria are carried out by cilantrones. Cilenterone performs physiological functions such as digestion, transport of nutrients, respiration, excretion, excretion of waste products, etc. Food material is taken up in the cilantro and extracellular and intracellular digestion is carried out. Undigested food and waste products are excreted through the stomata. So Cilenteron is called Gastrovascular cavity or Gastrovascular cavity. Dr. Siddiq Publications
Importance of Coelenteron
1. Cilantron contains food.
2. It causes extracellular digestion.
3. Food and excreta are transported through it.
4. It excretes waste through the stoma.

1. Cilantron contains food.
2. It causes extracellular digestion.
3. Food and excreta are transported through it.
4. It excretes waste through the stoma.

Both alimentary canal and body cavity functions of Nidaria are carried out by cilantrones. Cilenterone performs physiological functions such as digestion, transport of nutrients, respiration, excretion, excretion of waste products, etc. Food material is taken up in the cilantro and extracellular and intracellular digestion is carried out. Undigested food and waste products are excreted through the stomata. So Cilenteron is called Gastrovascular cavity or Gastrovascular cavity. Dr. Siddiq Publications

The body cavity of animals of the order Nidaria is called a coelenteron. The body cavity of the Hydra is the Cilantron. Archenteron transforms into Cilenteron. It is covered by gastrodermis. It involves extracellular digestion. Food and excreta are transported through it. Hence it is called Gastrovascular cavity. Cilantron is sometimes called blind gut or blind sac. It is exposed through the stoma. Takes food and leaves waste through mouth. Dr. Siddiq Publications

Nematocyst initiation is a chemical and mechanical process. When a prey comes close to the hydra’s attractor, the trigger is thrown. Chemicals in the prey’s body increase the water permeability of the hydra’s nematocyst wall. The osmotic pressure or hydrostatic pressure of the capsule increases. Water quickly enters the bag. A chemical called poly-ℽ-glutamate is secreted inside the sac. The operculum opens as soon as the prey touches the nidocile. Sutraka is thrown out with lightning speed. This entire event takes place in just 3 milliseconds.
Once the nematocyst is released, it cannot be returned to the nematocyst. That is, once thrown, it cannot be used again. No more nematocysts are formed in the same nidocyte. Such nidocytes slowly enter the gastrointestinal tract and are mixed with food and digested. Within 48 hours new nidocytes are generated and used.

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.

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.

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.

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.

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.