Why do arthropods make up such a large share of estimated species diversity?

Arthropods represent the largest phylum in the animal kingdom, accounting for approximately 84 percent of all described animal species. Their immense diversity and success are primarily attributed to several key evolutionary adaptations:1

• The Exoskeleton: Arthropods possess a rigid, jointed exoskeleton composed of chitin. This structure serves a dual purpose: it provides essential support for movement and acts as a protective, waterproof barrier that prevents dehydration. This adaptation allowed arthropods to successfully invade and diversify across nearly all terrestrial habitats.23
• Locomotory Versatility: The combination of a jointed skeleton and specialized muscles enables a wide range of precise movements, including running, digging, climbing, and flight—a capability unique among invertebrates.34
• Segmented Body Plan: The arthropod body is typically segmented, a trait inherited from ancestral forms that facilitates efficient movement and specialization of body parts.13
• Ecological Ubiquity: Arthropods are found in every environment on Earth, from deep-sea habitats to high-altitude mountain peaks and extreme desert conditions. This ability to exploit diverse ecological niches has driven significant speciation.14

While roughly one million species have been described, zoologists estimate that millions more remain undiscovered, particularly in tropical forest canopies.1