The imperial shrimp, Periclimenes imperator, is sometimes seen riding on the back of large sea cucumbers. The shrimp gets to move around to areas with food and expend very little energy, while the sea cucumber is unaffected. What type of relationship is this, and why

Commensalism

Explanation:

Commensalism is a form of nutritional relationship between tow living organisms in which one of the organisms (the commensal) benefits and the other is unaffected in any way.

In this case, the shrimp benefit from the sea cucumber by getting its shelter and get moved around while the sea cucumber is not in any way affected.

Commensalism, because one species benefits