The word Cnidoblast is derived from the Greek words knide meaning nettle and blastos meaning germ. The goblet or flax-shaped cells on the exterior of hydra are called nidoblast cells. It can be round, oval, pear-shaped, cup-shaped or oval-shaped. Nidoblast cells are found everywhere in the body except the soles of the feet. But its number is more in Karshika. Sometimes the cells are arranged in clusters. A group of them is called a battery.
1. Integument: Each nidoblast cell is covered by a bilayered envelope. Outer cover and inner cover. It is composed of proteins and lipids. Between the two envelopes are granular cytoplasm, a nucleus, mitochondria, lysosomes, ribosomes, etc.
2. Nematocyst: Small cysts with twisted secretions present in nidoblast cells are called nematocysts. The sac of nematocyst is called capsule. Capsules contain the poisonous liquid hypnotoxin. Hypnotoxin is composed of proteins and phenols. Hypnotoxin poison is neurotoxic in nature. That is, it acts on the victim’s nervous system. The level of this venom is 75% similar to that of a gokra or cobra snake. The nematocyst has a long and hollow filament at its tip. The broad part of the base of the sutraka is called the butt or shaft. The butt has three large spines called barbs. The butt consists of spirally arranged small barbule spines. Normally, the nematocyst is inserted into the sac with butts and spines. A nematocyst once shed never reenters.Dr. Siddiq Publications
3. Operculum: The mouth of nematocyst has a lid like part. It is called operculum. It moves sideways when exposed.
4. Nidocile: The free end of the nidocyte cell consists of a tough, firm, tiny and hypersensitive hollow spine. It is called nidosil. It is a transformed cilium. It works like a trigger. As a result, patched sutraka is thrown out. Dr. Siddiq Publications
5. Muscle fibers and lasso: Several muscle fibers emerge from the lower end of the nematocyst. Besides, there is a twisted thread called lasso at the lower end.
