Invertebrate zoology is a sub-discipline of zoology that is concerned with the invertebrates. Invertebrates are animals that lack a vertebral column (a backbone) as opposed to animals that possess it such as fish, amphibians, reptiles, birds, and mammals. Animals that lack a backbone include sponges, echinoderms, tunicates, mollusks, arthropods, etc. Protists (single-celled eukaryotes) are not regarded as invertebrates and are dealt with in another field, i.e. protistology. Thus, the invertebrate zoology includes most animal groups with the exception of those belonging to the subphylum Vertebrata.
Because of the diverse groups of animals included in invertebrate zoology, this field can be further subdivided into the following sub-disciplines: (1) arthropodology, (2) cnidariology, (3) helminthology, and (4) invertebrate paleontology. Arthropodology is a subdiscipline that deals primarily with arthopods. This subdiscipline may be further subcategorized into arachnology (studies spiders and other arachnids), entomology (studies insects), carcinology (studies crustaceans), and myriapodology (studies centipedes, millipedes, and myriapods). Cnidariology deals with studying the cnidarians. The subdiscipline that is concerned with parasitic worms is called helminthology. The subdiscipline that studies the extinct and fossil invertebrates is called invertebrate paleontology.