Invertebrates make up 96% of the described animal kingdom (by species). Traditionally, among the Metazoa (animals), invertebrates comprise 1) the species of the phylum Chordata that do not belong to the subphylum Vertebrata and 2) the species of all other phyla.
The major events leading to the diversification of invertebrates occurred in late Proterozoic and early Cambrian seas.
—September 2020
Lance Jones 