thread-cell

from The Century Dictionary.

• noun One of the little bodies or cavities of a cœlenterate, as a jellyfish or sea-nettle, containing a coiled elastic thread that springs out with stinging effect when the creature is irritated; an urticating-organ; a nematocyst; a lasso-cell; a cnida.
• noun An occasional name of a seed-animalcule or spermatozoön.