Algae is often is symbiosis with sponges which is the reason many sponges are green. Phylum Cnidaria Cnidarians include the jellyfish, hydras, corals, and sea anemones. They have radial symmetric and tissues but no organs. The name cnidarian comes from the stinging cells called cnidocysts that every cnidarian has. The tissues form two layers which include the ectoderm and endoderm.
Cnidarians have two general body plans.
The first is that of a medusae, and the second is that of a polyp. Like the sponges, cnidarians also often have a mutualism with algae.