Jellyfish (phylum Cnidaria, including jellyfish, corals and sea anemones) may look like the “simplest” of animal phyla after sponges.
Ironically, the rarity of genes and proteins in sequence space means that even thirty million years is not nearly enough time for the neo-Darwinian mechanism to generate a new gene or protein, much less a new animal form.
A while back at Jerry Coyne’s blog, Why Evolution Is True, contributor Greg Mayer wrote a post encouraging readers to buy a new 2013 book about the Cambrian explosion.
“Evolutionary change isn’t supposed to happen so abruptly, at least not according to Charles Darwin.”
Lava produces cavities, and a sponge or Swiss cheese produces cavities, but that doesn’t imply they have any “physico-genetic” relationship.