The first animals that began to move were mobile toroids... jellyfish, which belong to the phylum cnidaria (also known as coelenterates because of their radial rather than bilateral shape). They appeared 500 million years ago, in the well-known Cambrian explosion of life, and continue to populate the seas today. The most fundamental work of the Universe, made biology so that we can admire it and learn from it. Want to learn with us? Sign up for Resonance Academy... it's free! We are waiting for