Hi Carol, When I took undergrad invertebrate zoology, most of the textbooks stated that there were "somewhat over 80,000 described species of Mollusca". However, that was shortly after mollusks were discovered. Most of what I have read recently puts the number somewhere between 100,000 and 120,000 described species. Of course, not all of them have shells, but most do. The same old textbook says there are an additional 35,000 described fossil species. I wouldn't be surprised if that number has increased by a factor greater than that of the living species. The mollusks are the second largest phylum of animals, exceeded in numbers only by the Arthropods. Of course, the Arthropods get top billing largely thanks to the inclusion of that one mega-class of animals we all know and love so well - the insects. Paul M.