Nematocyst

A pressurized capsule inside a cnidocyte that rapidly ejects a thread. Its discharge can pierce, entangle, or adhere to prey and threats.

Cnidocyte: A specialized cell in cnidarians that contains an organelle capable of rapid discharge. The nematocyst is the capsule housed inside this stinging cell.
Cnidaria: A phylum of aquatic animals that includes jellyfish, corals, sea anemones, and hydras. Nematocysts are characteristic structures of this animal phylum.
Predation in cnidarians: The capture and consumption of prey by animals in the phylum Cnidaria. Nematocysts immobilize or retain prey before it is brought to the mouth.
Portuguese man o' war: A colonial hydrozoan whose long tentacles bear venomous stinging cells. Its tentacle nematocysts can cause painful stings in humans.
Nematocyst discharge: The rapid eversion of a nematocyst’s coiled tubule after stimulation. This process converts stored capsule pressure into a deployed thread.
Capsule (cnidarian): The enclosed chamber of a cnidarian stinging organelle, containing its coiled tubule and fluid. This chamber stores the components and pressure needed for discharge.
Cnidarian defense: Protective behaviors and structures used by cnidarians against predators and other threats. Discharging nematocysts can deter contact or injure an attacker.
Box jellyfish: A group of cubozoan jellyfish with cube-shaped bells and tentacles bearing nematocysts. Their stinging capsules can deliver potent venom to prey and people.
Cnidocil: A hairlike sensory structure associated with a cnidocyte that can trigger discharge. Mechanical stimulation of this structure can initiate capsule firing.
Operculum: A lid-like structure that covers the opening of some nematocyst capsules. In capsules with an operculum, its opening permits the tubule to emerge.

Linked from 13 pages