Nonarthropod

Nonarthropod is a non-formal term used in biology to refer to any organism that is not an arthropod. In common zoological use, it contrasts with the phylum Arthropoda, which includes insects, arachnids, crustaceans, and myriapods. The term thus designates all other animals outside Arthropoda and is often used in comparative anatomy, ecology, and paleontology as a broad, convenience category rather than a clade.

Nonarthropods span many phyla and lineages and include vertebrates (such as mammals, birds, reptiles, amphibians, and fishes) as well as invertebrate groups like Mollusca (snails, clams, octopuses), Annelida (earthworms, leeches), Echinodermata (starfish, sea urchins), Cnidaria (jellyfish, corals), Porifera (sponges), Placozoa, and Ctenophora (comb jellies), among others. Nematodes and nemertines, flatworms, and other lesser-known phyla also fall outside Arthropoda. Because Arthropoda is the most diverse animal lineage, the nonarthropod category covers a vast range of body plans, ecologies, and life histories.

Taxonomically, nonarthropod is not a monophyletic group; it is a convenience label used for contrasting with arthropods and is not itself a formal taxonomic rank. Research on nonarthropod animals contributes to understanding the evolution of body plans, sensory systems, and development across the animal kingdom.

See also: Arthropoda, Animalia.