Final answer:
The phylum with the greatest number of known species is Arthropoda, which includes classes like insects, crustaceans, and myriapods, and is known for its jointed appendages and chitin exoskeleton.
Step-by-step explanation:
The Animal Phylum that contains the greatest number of known species is Arthropoda. The name "Arthropoda" means "jointed legs", reflecting one of their defining characteristics. The phylum Arthropoda dominates the animal kingdom, making up an estimated 85 percent of known species, with many still to be discovered or described. All arthropods share common features: a segmented body, jointed appendages, and an exoskeleton principally made of chitin, which is part of their success in colonizing various habitats. Among the arthropods, insects constitute the largest group.
Arthropods encompass various classes, including Myriapoda (centipedes and millipedes), Hexapoda (insects and their relatives), Crustacea (crabs, lobsters, crayfish, barnacles), among others. The remarkable diversity and adaptive capabilities of arthropods have allowed them to thrive in terrestrial, aquatic, and aerial environments. This phylum is considered the most speciose in the animal kingdom due to its vast number of species compared to other phyla such as Nematoda, Cnidaria, Mollusca, and Chordata.