Invertebrate zoology is the biological discipline that consists of the study of invertebrate animals, i.e. animals without a backbone (a structure which is found only in fish, amphibians, reptiles, birds and mammals.)
Invertebrates are a vast and very diverse group of animals that includes sponges, echinoderms, tunicates, numerous different phyla of worms, molluscs, arthropods and many additional phyla. Single-celled organisms or protists are usually not included within the same group as invertebrates.
Invertebrates are 97% of all named animal species, and because of that fact, this subdivision of zoology has many further subdivisions, including but not limited to:
These divisions are sometimes further divided into more specific specialties. For example, within arachnology, acarology is the study of mites and ticks; within entomology, lepidoptery is the study of butterflies and moths, and so on.