|MadSci Network: Zoology|
You can get this sort of information out of most college introductory biology texts, including The Living World by George Johnson. It covers invertebrates (including insects, worms and starfish) in chapter 18, and vertebrates (including fish, birds, mammals, reptiles and amphibians) in chapter 19, giving the numbers of species in each group, which you could then use to rank them. You can also access these chapters via the web:
Try the links in the MadSci Library for more information on Zoology.