Arthropodan is an adjective used to describe animals that belong to the phylum Arthropoda. This phylum includes creatures such as insects, crustaceans, and arachnids. While there are few synonyms that directly relate to the word arthropodan, there are many related terms that could be used instead. For example, the word invertebrate is often used to describe animals without a backbone and could be used when referring to arthropods. Another related term would be exoskeleton, as arthropods are known for their hard outer shells. Lastly, the words chelicerate and myriapod could be used to describe specific types of arthropods, such as spiders and millipedes, respectively.