What is a trait you would use to classify fish as belonging either the phylum chordata or arthropada?

Fish belong to the phylum chordata, while arthropods belong to the phylum arthropoda. One trait that can be used to classify fish as belonging to the phylum chordata is the presence of a notochord. A notochord is a flexible, rod-shaped structure that runs along the dorsal side of the body and provides support. All chordates have a notochord at some point in their life cycle, while arthropods do not. Other traits that are characteristic of chordates include a dorsal nerve cord, pharyngeal slits, and a post-anal tail.