Filter feeders can play an important role in condensing biomass and removing excess nutrients (such as nitrogen and phosphate) from the local waterbody, and are therefore considered water-cleaning ecosystem engineers.

Filter feeders can be sessile, planktonic, nektonic or even neustonic (in the case of the buoy barnacle) depending on the species and the niches they have evolved to occupy.

Extant species that rely on such method of feeding encompass numerous phyla, including poriferans (sponges), cnidarians (jellyfish, sea pens and corals), arthropods (krill, mysids and barnacles), molluscs (bivalves, such as clams, scallops and oysters), echinoderms (sea lilies) and chordates (lancelets, sea squirts and salps, as well as many marine vertebrates such as most species of forage fish, American paddlefish, silver and bighead carps, baleen whales, manta ray and three species of sharks—the whale shark, basking shark and megamouth shark).

[6] Manta rays can time their arrival at the spawning of large shoals of fish and feed on the free-floating eggs and sperm.

[8] Mysidaceans live close to shore and hover above the sea floor, constantly collecting particles with their filter basket.

A baleen is a row of a large number of keratin plates attached to the upper jaw with a composition similar to those in human hair or fingernails.

These plates are triangular in section with the largest, inward-facing side bearing fine hairs forming a filtering mat.

Their baleen plates are narrow and very long — up to 4 m (13 ft) in bowheads — and accommodated inside the enlarged lower lip which fits onto the bowed upper jaw.

[16] Baleen whales typically eat krill in polar or subpolar waters during summers, but can also take schooling fish, especially in the Northern Hemisphere.

Suspended food (phytoplankton, zooplankton, algae and other water-borne nutrients and particles) are trapped in the mucus of a gill, and from there are transported to the mouth, where they are eaten, digested and expelled as feces or pseudofeces.

Scientists believe that the Chesapeake Bay's once-flourishing oyster population historically filtered the estuary's entire water volume of excess nutrients every three or four days.

[19] Nutrient removal by shellfish, which are then harvested from the system, has the potential to help address environmental issues including excess inputs of nutrients (eutrophication), low dissolved oxygen, reduced light availability and impacts on eelgrass, harmful algal blooms, and increases in incidence of paralytic shellfish poisoning (PSP).

For example, the average harvested mussel contains: 0.8–1.2% nitrogen and 0.06–0.08% phosphorus[20] Removal of enhanced biomass can not only combat eutrophication and also support the local economy by providing product for animal feed or compost.

In Sweden, environmental agencies utilize mussel farming as a management tool in improving water quality conditions, where mussel bioextraction efforts have been evaluated and shown to be a highly effective source of fertilizer and animal feed[21] In the U.S., researchers are investigating potential to model the use of shellfish and seaweed for nutrient mitigation in certain areas of Long Island Sound.

They are useful as they are sessile, which means they are closely representative of the environment where they are sampled or placed (caging), and they breathe water all the time, exposing their gills and internal tissues: bioaccumulation.

Water is expelled through a single osculum at a velocity of about 8.5 cm/second: a jet force capable of carrying waste products some distance away from the sponge.

Their oddly shaped beaks are specially adapted to separate mud and silt from the food they eat, and are uniquely used upside-down.

The filtering of food items is assisted by hairy structures called lamellae which line the mandibles, and the large rough-surfaced tongue.

Traditionally, Ctenochasmatoidea as a group has been listed as filter-feeders, due to their long, multiple slender teeth, clearly well adapted to trap prey.

Other ctenochasmatoids lack these, and are now instead thought to have been spoonbill-like catchers, using their specialised teeth simply to offer a larger surface area.

[28] Boreopterids are thought to have relied on a kind of rudimentary filter feeding, using their long, slender teeth to trap small fish, though probably lacking the pumping mechanism of Pterodaustro.

[32] Stomatosuchidae is a family of freshwater crocodylomorphs with rorqual-like jaws and minuscule teeth, and the unrelated Cenozoic Mourasuchus shares similar adaptations.