The correct answer is: Arthopoda.
Arthropods are the largest phylum in the animal kingdom, with over 8.7 million known species. They are characterized by a segmented body, jointed appendages, and an exoskeleton made of chitin. Arthropods include insects, spiders, crustaceans, and millipedes.
Annelida are a phylum of segmented worms that includes earthworms, leeches, and marine worms. They are characterized by a long, cylindrical body that is divided into many segments. Annelids have a closed circulatory system and a digestive system that runs the length of their body.
Chordates are a phylum of animals that includes vertebrates, such as fish, amphibians, reptiles, birds, and mammals. They are characterized by a notochord, a rod-shaped structure that supports the body. Chordates also have a dorsal hollow nerve cord and a post-anal tail.
Protozoa are a phylum of single-celled organisms that includes amoebas, paramecia, and ciliates. They are characterized by a lack of a cell wall and a nucleus. Protozoa are found in a variety of habitats, including water, soil, and the human body.
In conclusion, the largest phylum in the animal kingdom is Arthropoda.