Summary:
- Cnidarians are invertebrates such as jellyfish and corals.
- They belong to the phylum Cnidaria.
- There are more than 10,000 cnidarian species.
- They are a little more complex than sponges.
- They have radial symmetry and tissues.
- They may exist in the polyp (left) or medusa (right) form.
- Some species alternate between polyp and medusa forms.
- Other species exist in just one form or the other.