(n.) A phylum is a group of one or more classes of animals that share a number of common characteristics. The plural of phylum is phyla. Some phyla found in New Mexico are the Chordata (which include mammals, birds, reptiles, amphibians, and fishes), the Arthropoda (insects, crayfish, spiders, etc.), and the Mollusca (snails and clams). The phylum is thus a level of classification smaller than a kingdom, but larger than a class. The equivalent level of classification among plants is called a division.