Animals in the phylum Cnidaria are often classified into four classes: Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa. “Cnidaria” means “stinging nettle,” and animals are classified in this phylum for possessing stinging cells called nematocysts.
Hydrozoa - Siphonophores and Hydra (3,600 species) (Photo source)
Scyphozoa - Jellyfish (228 species) (Photo source)
Cubozoa - Box Jellies (42 species) (Photo source)
Anthozoa - Sea Anemones, Corals, and Sea Pens (6,100 species) (Photo source)