What is the most diverse phylum?

• A. Arthropoda
• B. Chordata
• C. Mollusca
• D. Echinodermata

Answer: (A)

Diversity in this context comes from the sheer number of species and the variety of forms and lifestyles a group has evolved. Arthropods win here because they have a highly modular body plan—segmented bodies, jointed appendages, and a tough exoskeleton—that can be modified in countless ways. Insects alone account for the vast majority of described species, with well over a million named species and many more likely yet to be described. This enormous species richness is paired with extraordinary ecological versatility: wings enable rapid dispersal and colonization of new habitats; metamorphosis creates separate life stages that exploit different resources; a wide array of mouthparts supports numerous feeding strategies; and adaptations span from forest canopies to deserts, freshwater to deep sea. While the other phyla have impressive diversity, none match the explosive radiation of arthropods, especially insects, across habitats and niches.