A segmented body is a key characteristic of which animal phylum?

• A. Annelida
• B. Cnidaria
• C. Nematoda
• D. Porifera

Answer: (A)

Segmentation, or metamerism, is the division of the body into repeating units called segments. This pattern is a hallmark of annelids, the segmented worms such as earthworms, leeches, and polychaetes. In these animals the body is built from many similar ring-like segments, each housing parts of the digestive, nervous, and circulatory systems, with septa often separating the segments and forming a true coelom. This arrangement supports flexible movement and allows specialization of body regions through the repeating units. In contrast, cnidarians have radial symmetry and no segmentation, nematodes are unsegmented and have a pseudocoelom, and poriferans lack true tissues and organized body plans, so none of them exhibit true segmentation like annelids do.