The characteristic feature of animals belonging to the phylum Annelida is the segmented body structure. Annelids, such as earthworms and leeches, have bodies that are divided into repeated segments, which allows for more efficient movement and a higher degree of complexity in their structure.
The phyla Cnidaria (such as jellyfish), Echinodermata (such as starfish), and Porifera (such as sponges) do not exhibit segmentation. Therefore, the correct answer is Annelida, which is known for its segmented body plan.