Cnidocytes or Stinging cells are organs of offence and defence of coelenterates. They are inter spaced singly between epithelio-muscular cells. Each cnidoblast bears a sensory bristle or cnidocil and a bladder or sac called nematocyst. They are of following types
(i) Penetrants or Stenoteles They are largest of all. Its nematocyst contains a poisonous proteinaceous fluid called hypnotoxin. They are mainly used for offence and defence.
(ii) Streptoline glutinant These are smaller and elleptical also known as large or holotrichous isorhizas.
(iii) Volvent or desmonemes These are the smallest nematocytes. They help in capturing prey.
(iv) Small glutinant or steroline glutinant or atrichous isorhizas:
These are still smaller, somewhat elleptical with spineless open thread and are used in locomotion and food capturing.