Nematocysts: It is stinging organ of coelenterates. It is produced inside a stinging cell called nematoblast or cnidoblast which comprises hypnotoxic fluid and a long coiled tube for injecting the fluid into prey or predator. It is used as an organ of offence and defence.
Polyp : It is a free living sessile or mobile zooid or individual of a simple or colonial coelenterate. It is cylindrical in outline with a terminal mouth surrounded by a ring of tentacles, e.g., Hydra, Physalia, coral.
Medusa : It is a bell-like or umbrella-shaped free floating or swimming individual (zooid) of coelenterates.
Mesoglea : It is a non-cellular gelatinous middle layer found between ectoderm and endoderm as in coelenterates.
Planula : This is a free swimming young ovoid ciliated larva of coelenterates. It gives rise to the adult individual.
