nem·a·to·cyst 
(nĕmə-tə-sĭst′, nĭ-mătə-)
(nĕmə-tə-sĭst′, nĭ-mătə-)n.
A capsule within specialized cells in the tentacles of cnidarians, such as jellyfish and corals, containing a barbed, threadlike tube that delivers a toxic sting to predators and prey.
nem′a·to·cystic adj.