The correct answer is option 3, Phylum Annelida. Phylum Annelida consists of segmented worms, such as earthworms and leeches. These organisms have body segmentation, which means that their bodies are divided into a series of repeated segments. Each segment typically contains similar structures, such as muscles, nerves, and organs. This segmentation allows for specialization and flexibility in movement.

Option 1, Phylum Mollusca, is incorrect. Mollusks, such as snails and clams, do not have segmented bodies.

Option 2, Phylum Arthropoda, is incorrect. Arthropods, such as insects and crustaceans, have a body that is divided into segments, but the segments are fused and specialized, rather than independently movable like in annelids.

Option 4, Phylum Cnidaria (formerly Phylum Coelenterata), is incorrect. Cnidarians, such as jellyfish and coral, do not have segmented bodies.

Therefore, the correct answer is option 3, Phylum Annelida.