Which one of the following is a filter feeder?

The correct option is Oyster.

Explanation:

Filter feeders are organisms that feed by straining suspended matter and food particles (such as plankton and algae) from water, typically by passing the water over a specialized filtering structure.

Let us analyze the given choices:

1. Oyster: Oysters are bivalve mollusks that feed by pumping water through their gills. The specialized cilia on their gills trap microscopic organisms and organic particles from the water column, making them classic examples of filter feeders.
2. Catfish: Catfish are mostly bottom feeders or predators, feeding on insects, fish, and detritus.
3. Octopus: Octopuses are active predators that hunt prey such as crabs, fish, and mollusks using their arms and beak.
4. Pelican: Pelicans are fish-eating birds that catch their prey using their large throat pouches, which function as scoop nets rather than filter-feeding mechanisms.

Therefore, among the options provided, the Oyster is a filter feeder.