Cnidarians (Coelenterates) are a phylum of predominantly marine species whose distinguishing feature is cnidocytes: specialised cells that they use mainly for capturing prey.

Rhizostoma pulmo (Barrel Jellyfish)	Cyanea lamarckii (Blue Jellyfish)
Actinia equina (Beadlet Anemone)	Anemonia viridis (Snakelocks Anemone)

Useful links:

Marine Life Information Network (MarLIN)