Explanation

Filter feeders are aquatic animals that obtain nutrition by straining suspended organic matter, plankton, and detritus from the water column through specialized anatomical filtering structures.

– Option C is correct: Oysters are sessile bivalve molluscs that function as critical biological filters in estuarine ecosystems. An individual adult oyster can pump and filter up to 50 gallons of water per day, passing it across its ciliated gills to trap microalgae, nutrients, and particulate impurities, thereby maintaining water clarity.
– Option A is incorrect: Catfish are predatory bottom-dwelling scavengers that detect food using sensory barbels.
– Option B is incorrect: Octopuses are active carnivorous cephalopod predators that hunt crabs, molluscs, and small fish.
– Option D is incorrect: Pelicans are piscivorous birds that capture fish by scooping water into their expandable throat pouches.

Hence, the filter feeder is the Oyster — Option C.