A diagram in the course handout shows that a tiny capsule inside a cnidarian stinging cell everts a thread when triggered. Identify the related structure or process.

A nematocyst is the stinging capsule within a cnidocyte. Its rapid discharge helps immobilize prey and is one of the diagnostic features of phylum Cnidaria. This MCQ belongs to the Cnidaria topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.