noun, plural: nematocysts
Nematocytes are specialized cells found in the tentacles of Cnidarians (e.g. jellyfish, hydras, sea anemones, etc.). Each cell contains a large capsule organelle called nematocyst. Inside the nematocyst is a thread-like, coiled, hollow tube with toxic barbs. This tube is everted from the capsule to deliver a paralyzing sting to the target prey or enemies. Thus, nematocysts are chiefly for food gathering and defense mechanism of Cnidarians.
Word origin: Greek nēmat- (thread) + cyst