In what general way are mollusks more complex than roundworms?

Mollusks exhibit greater complexity than roundworms in several key aspects, including their body structure and organ systems. Mollusks possess a more advanced and diverse body plan featuring a coelom, a muscular foot, and a mantle that can produce shells, whereas roundworms have a simpler pseudocoelomate structure. Additionally, mollusks often have specialized organ systems, such as a complex circulatory system and a nervous system with more developed sensory organs, enabling them to interact more effectively with their environment. This complexity allows mollusks to occupy a wider range of ecological niches compared to roundworms.