Final answer:
Bivalves are filter-feeders that use gills to extract food from the water, which is digested in their stomach. They lack a radula, and instead, rely on the movement of cilia to move food particles to their mouth. Their feeding process contributes to the marine ecosystem, benefiting higher trophic levels and fisheries.
Step-by-step explanation:
Bivalves, such as clams, oysters, mussels, and scallops, gain food for nutrition through a process known as filter-feeding. These aquatic organisms have specialized structures-gills or ctenidia-that efficiently filter food particles from the water. Water flows into the bivalve's body through an incurrent siphon, passes over the gills where food particles are trapped in mucus, and then transferred by cilia to the mouth. Afterward, the food is digested in the stomach. Bivalves lack a head and a radula, which is commonly found in other mollusks for feeding. Instead, they rely on this filter-feeding mechanism to capture plankton and organic matter suspended in the water.
Beyond nutrition for themselves, bivalves play a significant ecological role by enhancing nutrient flux to higher trophic levels and acting as natural water filters, which can indirectly boost local fisheries and help control eutrophication. Their beds serve as vital nursery areas for other marine species, including commercially important fish, and provide a complex habitat that supports a diverse marine ecosystem.