Other key changes from the First Edition (1990) include:
* the incorporation of new developments in phylogenetics, developmental biology, and molecular genetics
* major changes at the highest levels among the invertebrates. Three phyla that appeared in the original bookPentastomida, Pogonophora, and Vestimentiferano longer exist, and a new phylum, Cycliophora, has been erected. Moreover, this edition discusses recent work in molecular systematics that has shaken classic views on animal classification.
* a large new section on "Kingdom Protista" (replacing "Protozoa") containing new contemporary views of these organisms (arranged in 18 phyla).