cnidarians – aquatic invertebrates with a single body opening (works as mouth and anus) and typically tentacles

(Pronounced nuh-dair-ee-un (the stress on the dair))

Note: The best known example of cnidarians is a jellyfish.

To remember the meaning of cnidarians, use the following mnemonic:

A number of dairy cows went underwater (cnidarians) to play with the jellyfish in the aquarium (aquatic).

Cnidarians are also known as coelenterates. The 'c' in the word cnidarians is not pronounced because cn is not an allowable consonant cluster in English, so the 'c' is always silent. 

For further information see coelenterates.