Pronunciation: ne-MA-to-sist

Etymology: The term is derived from two Greek roots that mean thread (nema, νήμα) and bladder (kysti, κύστη). The reference is to the thread-like protrusion of a discharged nematocyst (see below).

Nematocysts (=cnidae) are specialized structures in the Cnidaria that function in food capture, attachment, defense, etc. They are very complex structures that are formed within special cells called cnidoblasts and discharge by physical or chemical stimulation. The illustration below shows a discharged nematocyst within a cnidoblast.

By Jack R. Holt. Last revised: 01/02/2009