Which one of the following phylum having animal with radial symmetry ?

Question

Accepted Answer

Option 3, Echinodermata, is the correct answer because animals in this phylum exhibit radial symmetry, particularly in their adult forms. Radial symmetry means that the body plan of the organism can be divided into similar halves by multiple planes passing through the central axis. Echinoderms, such as starfish, sea urchins, and sea cucumbers, typically have a body structure that radiates from a central point, which is a hallmark of radial symmetry.

1. **Explanation for Option 3 (Echinodermata):**
   - Echinoderms are known for their unique water vascular system and their radial symmetry, which is most evident in their adult stage. This symmetry allows them to interact with their environment from all sides equally, which is advantageous for their sessile or slow-moving lifestyle. The radial symmetry in echinoderms is a key characteristic that distinguishes them from many other animal phyla.

2. **Explanation for why other options are incorrect:**

- **Option 1 (Arthropoda):** 
     - Arthropods, including insects, arachnids, and crustaceans, exhibit bilateral symmetry, not radial symmetry. Bilateral symmetry means the body can be divided into two identical halves along a single plane, which is typical for animals that have a distinct head and tail region and are more active in their movement.

- **Option 2 (Annelida):**
     - Annelids, such as earthworms and leeches, also display bilateral symmetry. Their bodies are segmented and elongated, which is characteristic of bilateral symmetry, allowing for more efficient movement and a streamlined shape.

- **Option 4 (Platyhelminthes):**
     - Platyhelminthes, or flatworms, are another group of animals that exhibit bilateral symmetry. They have a flattened body plan that is symmetrical along one plane, which is typical for organisms that have a defined head and tail region.

In summary, Echinodermata is the only phylum among the given options that features animals with radial symmetry, particularly in their adult forms, making Option 3 the correct choice.