Final answer:
Bivalves in Class Bivalvia do not have a radula; they are filter-feeders that use gills for feeding and respiration, characterized by a mantle, a shell, and open circulation. So the correct option is B.
Step-by-step explanation:
The question asks which of the listed options is not a structure or characteristic of members of the Class Bivalvia in the Phylum Mollusca. Bivalves are known for several distinctive attributes, including a mantle that secretes their shell, a shell for protection, gills (ctenidia) for respiration, and open circulation. However, unlike other mollusks, bivalves do not have a radula, which is typically a rasping feeding organ. Therefore, the correct answer to the question is B. A radula since bivalves are filter-feeders that lack this structure.