Invertebrates starts with an introduction to the topic. It considers systematics, phylogeny, and classification. It also looks at the animal kingdom. Two basal metazoan phyla, porifera and placozoa, are examined. Other topics include phylum cnidaria, phylum ctenophora, bilateria, and phylum xenacoelomorpha. The text also looks at flatworms, four enigmatic protostome phyla, phylum nemertea, phylum mollusca, and phylum annelida. It examines spiralian phyla, the gnathifera, lophophorates, nematoida, scalidophora, and the emergence of the arthropods. It then delves into phylum arthopoda in detail. It looks at deuterostomes and the phylum echinodermata, phylum hemichordata, and phylum chordata.