Question

Name the two animal phyla which exhibit radial symmetry.

Answer 1

Hint: The radial symmetry is the type of the symmetry in which the animal body has the equal mirror when it is divided in all the planes. This type of symmetry is opposite to the bilateral symmetry in which the body is divided into the two equal halves in a single plane.

Complete Answer:
- The cnidarians and the echinoderms possess the radial symmetry. Cnidarians are also called coelenterate that belong to the phylum Cnidarian (Coelenterate). This phylum comprised 9000 living species.
- Generally in marine animals, the cnidarians include the corals, hydras, jellyfish, Portuguese men-of-war, ocean anemones, ocean pens, ocean whips, and ocean fans.
- Cnidarians are radially even and they do not possess cephalization (convergence of sensory organs in a head), their bodies have two cell layers instead of the three like the higher animals.
- And they possess the saclike coelenteron body that has only opened (the mouth). Cnidarians have two body structures—polyp and medusa—which frequently happen in its life cycle.
- Echinoderms are a significant group of marine animals. There are around 7000 species and they possess various colors in their body.
- Echinoderms have more arms for their balance. They have a shell, made basically of calcium carbonate, which is secured by skin.
- The skin contains cells for the maintaining and supporting the skeleton, shade cells, cells to recognize movement on the animal's surface. The organ cells in them emit clingy liquids or even poisons.

Thus cnidarians and the echinoderms exhibit radial symmetry.

Note: The cnidarians engulf its food by the opening and after digestion the waste are excreted through the same opening. They lack the proper circulatory system, they get the water and the nutrients through their skin. The examples of the echinoderms are the starfish, tube feet etc.