AIIMS 2018 Biology Phylum Mollusca MCQ Question

Option B is correct because Mollusca is characterized by the presence of a radula, a specialized feeding organ used for scraping or cutting food, and Dentalium is a genus of mollusks that possesses this feature. Option A is incorrect as Hemichordata do not have a true notochord; they possess a structure called a stomochord. Option C is incorrect because Platyhelminthes are acoelomate, meaning they lack a coelom, while Dugesia is a genus of flatworms. Option D is misleading since Coelenterata (now referred to as Cnidaria) includes both marine and freshwater species, and Hydra specifically is a freshwater organism.