The correct answer is: Arthropod.
Arthropods are the largest phylum of animals, comprising over 80% of all animal species on Earth. They are characterized by their jointed exoskeleton, segmented body, and paired appendages. Arthropods include insects, spiders, crustaceans, and millipedes.
Mollusca are the second largest phylum of animals, comprising about 8% of all animal species. They are characterized by their soft bodies, often protected by a hard shell. Mollusca include snails, slugs, clams, oysters, and octopuses.
Chordata are the third largest phylum of animals, comprising about 4% of all animal species. They are characterized by a notochord, a dorsal nerve cord, and pharyngeal slits. Chordata include vertebrates (animals with a backbone) and invertebrates (animals without a backbone).
Coelomates are animals that have a coelom, a body cavity that is lined with mesoderm. Coelomates include all animals except sponges, cnidarians, and flatworms.
In conclusion, the largest animal phylum is Arthropoda.