What term describes animals with jointed appendages and an external skeleton?

• A. Arthropod
• B. Invertebrate
• C. Mollusk
• D. Vertebrate

Answer: (A)

Arthropods are animals with jointed appendages and an external skeleton. This group includes insects, spiders, crustaceans, and more, and they’re defined by a segmented body plan, limbs that bend at joints, and an exoskeleton made of chitin that covers the organism. The exoskeleton protects them and helps reduce water loss, and they grow by molting since the hard outer shell doesn’t stretch. The other options don’t fit both features: invertebrates are a broad category of animals without a backbone, but not all lack jointed limbs or an exoskeleton; mollusks like snails and clams have soft bodies (often a shell) and not jointed appendages or an external jointed skeleton; vertebrates have internal skeletons.