As an evolutionary biologist, can I correct some of the misconcepts?
1. "Invertebrate" and "vertebrate" are actually not a scientific taxonomy term because "chordata" contain both vertebrate and invertebrate animals and in the phylogeny trees, invertebrate is actually polygenic group that represent more lineage with different evolutionary history.
2. As we had already debunk Aristotle's hierarchy of being that come from his book "historia animalium", it is not appropriate to say that certain animals are in "higher" hierarchy than other. while we can say that human maybe more evolutionary complex than sponges but it is wrong to say that human is in higher hierarchy than sponge because each lineage shares their unique evolutionary history since they diverge from another. Although the sponge may be morphologically similar to our ancestor, but in molecularly and physiologically, the sponge is totally different from the ancestor. In addition, all animal are evolutionary in highest ranking in their particular niche or the animals will be selected out by natural selection. Therefore, it is wrong to say that vertebrates are in higher ranking than invertebrate.
Lastly, I want to point out that there are actually five classes in cnidarian
1. Scyphozoa (common jellies such as the moon jelly)
2. Cubozoa (box jellies)
3. Hydrozoa (Portuguese Man-O-War, sea hydras)
4. Staurozoa (stalked Jellies)
5. Anthozoa (corals and sea anemones)