- The Class Hydrozoa are the most diverse group of cnidarians containing approximately 3700 species.
- Hydrozoa like all cnidarians have both polyp and medusa stages in their life cycles, and have symmetrical ovoids (body surface).
- Their life cycle is what distinguishes Hydrozoas compared to all other cnidarians.
- Hydrozoas can be found in marine- water environments except for in surfs
- They are most diverse and thriving in warm shallow waters, most likely reflecting the abundance of food source.