nematocyst

noun

1. A capsule, in certain cnidarians, containing a barbed, threadlike tube that delivers a paralyzing sting

   “Often one sees, on surface view, a distinctly rounded vacuole, occupying a position in the cell occupied in others by a large nematocyst.”

   “The young nematocyst decreases in size and becomes coarsely granular, the granules arranging themselves in a spiral line close under the external membrane.”

   “Nematocyst discharge is another example of the Rubicon principle – it either fires or it does not.”