Final answer:
A bristle worm living on a white sea urchin forms a commensal relationship where both species remain unaffected by each other.
Step-by-step explanation:
When a bristle worm lives on a white sea urchin, a commensal relationship is formed. In this type of relationship, the bristle worm benefits from using the sea urchin as a habitat without harming or benefiting the sea urchin. The sea urchin is unaffected by the presence of the bristle worm.
Learn more about Types of ecological relationships