What is cnidosac?
cnidosac meaning a sac located in a ceras of a nudibranch gastropod which contains undischarged nematocysts (obtained through feeding upon cnidarians) passed from the slug’s digestive system. When a predator attacks the nudibranch, the nematocysts may discharge as a defensive mechanism
Section through the ceras ofAeolidiopsis ransonishowing the cnidosac with three nematocysts. (Photo: Dr. Bill Rudman)
reference: Coral Reef Information System – Glossary