Which of the following invertebrates are characterized by having jointed legs?

Arthropods are indeed characterized by having jointed legs, which is one of the defining features of this large and diverse phylum. Arthropods include various species such as insects, arachnids (like spiders and scorpions), and crustaceans (such as crabs and lobsters). The jointed legs provide arthropods with a range of movement and adaptability, enabling them to thrive in various environments. This segmentation and jointed structure are key adaptations that contribute to their success as a group.

In contrast, other invertebrate groups listed do not share this characteristic. Mollusks, for example, typically have soft bodies with a muscular foot and may have shells, but they lack jointed limbs. Worms, which belong to the phyla Annelida (segmented worms) or Nematoda (roundworms), are elongated and do not possess jointed appendages, relying instead on body contraction for movement. Echinoderms, such as starfish and sea urchins, have a unique water vascular system and radial symmetry, and they are characterized by their tube feet rather than jointed legs. Therefore, the defining trait of jointed legs distinctly categorizes arthropods within the animal kingdom.