Which phylum is characterized by a segmented body?

Which phylum is characterized by a segmented body?

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

Answer: (A)

Segmentation, or metamerism, is the repeating series of body units along an organism’s length. Annelids—the worms with rings like earthworms and leeches—display true segmentation. Their body is made of many similar segments separated internally by septa, which allows each segment to specialize and coordinate movement. This metameric plan enables peristaltic locomotion and the organization of repeating structures (nervous, excretory, and muscular systems) within each segment, a defining feature of this group. The other choices don’t show this repeating, segmented pattern. Cnidarians have radial symmetry and simple tissue organization with no segmentation. Nematodes possess a single, unsegmented tube-like body plan. Porifera, or sponges, lack true tissues and organs and do not have segmented bodies.

Segmentation, or metamerism, is the repeating series of body units along an organism’s length. Annelids—the worms with rings like earthworms and leeches—display true segmentation. Their body is made of many similar segments separated internally by septa, which allows each segment to specialize and coordinate movement. This metameric plan enables peristaltic locomotion and the organization of repeating structures (nervous, excretory, and muscular systems) within each segment, a defining feature of this group.

The other choices don’t show this repeating, segmented pattern. Cnidarians have radial symmetry and simple tissue organization with no segmentation. Nematodes possess a single, unsegmented tube-like body plan. Porifera, or sponges, lack true tissues and organs and do not have segmented bodies.