The correct option is B. Hydra. Explanation of the Correct Answer Radial Symmetry Defined: Radial symmetry is a type of symmetry where the body plan of an organism can be divided into similar halves by multiple planes that pass through the central axis. This means that if you were to slice the organism in various ways through the center, each slice would look similar. Radial symmetry is commonly found in organisms that are sessile (fixed in one place) or free-floating, allowing them to interact with their environment from all sides. Why Hydra is Radially Symmetrical: - Body Structure: The Hydra is a small, freshwater organism belonging to the phylum Cnidaria. Its body is cylindrical and can be divided into similar halves along multiple planes. The tentacles, which are arranged around the mouth at one end, exemplify this symmetry. - Feeding and Movement: The radial symmetry of the Hydra allows it to capture prey from any direction, which is advantageous for its survival in aquatic environments. Explanation of Why Other Options are Incorrect A. Squid: - Symmetry Type: Squids belong to the class Cephalopoda and exhibit bilateral symmetry, not radial symmetry. This means that if you were to draw a line down the center of a squid, the left and right sides would be mirror images of each other. - Body Structure: Squids have a distinct head, a mantle, and arms that are arranged in a way that reflects bilateral symmetry, which is typical for more complex organisms that have a defined front and back. C. Snail: - Symmetry Type: Snails are also bilaterally symmetrical. They have a coiled shell and a body that can be divided into two equal halves along a single plane. The asymmetrical coiling of the shell can sometimes confuse people, but the overall body plan remains bilateral. - Body Structure: The head and foot of the snail are organized in a way that reflects bilateral symmetry, with a clear distinction between the front and back. D. Cockroach: - Symmetry Type: Cockroaches are another example of bilaterally symmetrical organisms. They have a body that can be divided into left and right halves that are mirror images. - Body Structure: The segmented body of a cockroach, with a distinct head, thorax, and abdomen, further emphasizes its bilateral symmetry. Summary of Key Points

• Radial Symmetry: Organisms like Hydra can be divided into similar halves along multiple planes through their central axis.
• Bilateral Symmetry: Squids, snails, and cockroaches exhibit bilateral symmetry, where the body can only be divided into two equal halves along one plane.
• Hydra's Adaptation: The radial symmetry of Hydra allows it to effectively capture prey from all directions, enhancing its survival in aquatic environments.

Revision Summary

• Radial symmetry allows for multiple planes of division, as seen in Hydra.
• Bilateral symmetry is characterized by a single plane of division, found in squids, snails, and cockroaches.
• Understanding body symmetry is crucial for classifying and studying animal behavior and adaptations.
• Always consider the organism's habitat and lifestyle when determining its symmetry type.