Skeletogenesis is a key morphogenetic event in the embryonic development of vertebrates and is of equal, although transient, importance in the development of the sea urchin, a marine invertebrate.[1] The larval sea urchin does not resemble its adult form, because the sea urchin is an indirect developer, meaning its larva form must undergo metamorphosis to form the juvenile adult. Here, the focus is on skeletogenesis in the sea urchin species Strongylocentrotus purpuratus, as this species has been most thoroughly studied and characterized.