What is the void found between the body of a mollusk and its mantle known as?

The space between the body of a mollusk and its mantle is called the mantle cavity. This cavity serves several important functions, including housing the gills and facilitating the exchange of gases and waste products, which is essential for respiration and excretion in aquatic mollusks. The mantle itself is a significant structure that secretes the shell (if present) and plays a vital role in the mollusk's overall body plan.

The other options do not accurately describe this space. The heart cavity does not refer to a distinct anatomical space in mollusks; rather, the heart is typically located within the coelomic cavity, which is separate from the mantle cavity. The term shell cavity might imply a space within the shell, but it does not denote the specific area between the body and the mantle. Lastly, while the gill cavity might seem relevant due to its association with respiration, it is actually part of the mantle cavity, which encompasses a broader area that includes the gills as well as serving other functions. Thus, mantle cavity is the correct term for this void in mollusks.