Nematocysts are found in Coelenterata.

Coelenterata, also known as Cnidaria, is a phylum of animals that includes jellyfish, sea anemones, and corals. Nematocysts are specialized cells found in the tentacles of these animals, which are used for defense and capturing prey.

Structure of Nematocysts:
Nematocysts are capsule-like structures that contain a coiled, hollow tube called a cnidocil. The tube is filled with venom and is used to paralyze prey or defend against predators. When triggered, the nematocyst capsule rapidly discharges the cnidocil, which pierces the target and injects the venom.

Functions of Nematocysts:
Nematocysts are used by Coelenterata for several purposes, including:
- Capturing prey: The nematocysts in the tentacles of jellyfish and other cnidarians are used to capture small fish and planktonic organisms.
- Defense: Nematocysts can also be used for defense against predators. When threatened, some cnidarians will release a cloud of nematocysts into the water, which can deter or injure the attacker.
- Movement: Some cnidarians, such as jellyfish, use nematocysts to propel themselves through the water.

Conclusion:
In conclusion, nematocysts are specialized cells found in the Coelenterata phylum, which are used for capturing prey, defense, and movement. They are a unique adaptation that allows these animals to survive in their aquatic environments.

Nematocytes are present in cnidarians which helps them to capture their prey because it contains stinging capsule which having hypanotoxin made up of glutathionone which is a toxin.