What is a defining feature of radial symmetry in organisms?

Radial symmetry is characterized by body parts that are arranged around a central axis, allowing for multiple planes of symmetry. This means that if you were to slice the organism through the center, you would get similar halves at various angles. This configuration is advantageous for organisms that are often found in aquatic environments, such as jellyfish and sea anemones, as it allows them to interact with their environment from all directions equally.

In contrast, the other options describe different types of symmetry or configurations. Splitting into two mirrored halves describes bilateral symmetry, which is common in organisms like humans and many animals, while having no defined shape could apply to certain amorphous organisms but does not define symmetry. Lastly, the arrangement of all body parts in a broadsheet does not accurately relate to the concept of symmetry at all. Therefore, the defining feature of radial symmetry is indeed the arrangement of body parts radiating from a central point.