All jellyfish are Cnidaria, an animal phylum that contains jellies, sea anemones, and corals, among others. There are more than 10,000 species of Cnidaria, and less than 4,000 of these are Medusazoa—those animals we think of as jellyfish. Those 4,000 jellyfish can be divided into four different groups.
The reason you have two sets of teeth probably comes down to size. A full set of permanent teeth would be too big to fit into a young child’s mouth. So milk teeth act as a bridge until the jaw is large enough to accommodate a full set of permanent teeth. The last teeth that emerge are your wisdom teeth.