Filter feeder

Filter feeders are special kinds of water animals. They eat tiny bits of food floating in the water. This food includes small living things like bacteria, microalgae, and zooplanktons. They have special parts that act like filters. These filters trap the tiny food as water passes through.

Filter feeders help keep water clean. By eating bits of organic material, they remove extra nutrients like nitrogen and phosphate from the water. This helps balance the health of water bodies.

Filter feeders come in many different shapes and live in many places. Some stay in one spot, while others float or swim. They include animals like sponges, jellyfish, corals, krill, clams, oysters, baleen whales, and manta rays. Some water birds, like flamingos, also act as filter feeders when they look for food in the water.

Vertebrates

Fish

Most forage fish are filter feeders. The Atlantic menhaden, a type of herring, eats plankton it catches in the water. Adult menhaden can clean up to four gallons of water each minute and help keep ocean water clear. They also help control the harmful red tide.

Some cartilaginous fishes are filter feeders too. The whale shark takes in water and traps tiny animals with special parts in its gills. The megamouth shark and basking shark also get small creatures from big amounts of water. Manta rays eat eggs and tiny animals when fish lay eggs.

Baleen whales

Baleen whales are whales with special plates in their mouths that work like filters. They use these plates to catch tiny animals like krill. These whales swim through groups of small creatures and use their baleen plates to catch food while letting water flow through. Their baleen plates are made of a material similar to human hair and help trap tiny food. Different kinds of baleen whales feed in different ways, but they all use their baleen to catch food.

Birds

Flamingos are birds that filter-feed on tiny shrimp. Their beaks are shaped to separate mud and silt from their food. They use special parts inside their beaks and their rough tongues to help filter food.

Prions are birds that also filter-feed, using the edges of their beaks to catch small creatures in the water.

Pterosaurs

Traditionally, a group called Ctenochasmatoidea was thought to be filter-feeders because of their long, slender teeth. However, only Pterodaustro could really pump water through its beak to trap food. Other types in this group probably caught food in a different way.

Boreopterids may have used their long, slender teeth to catch small fish, but they likely could not pump water like Pterodaustro.

Marine reptiles

Filter feeding was not common among Mesozoic marine reptiles, but a few may have been filter-feeders. Henodus was a reptile with special parts in its mouth that might have helped it filter tiny plants and algae from the water. Some other reptiles like members of Stomatosuchidae and Hupehsuchia also seemed able to filter-feed.

Lancelets

Lancelets (subphylum Cephalochordata) are fish-like chordates related to vertebrates. They live on the seafloor and burrow into sandy areas. Lancelets are filter feeders, eating tiny organisms and particles from the water.

Lancelets have special structures called buccal cirri, which are thin, tentacle-like strands in front of their mouths. These help them feel and filter food from the water. Water enters through the mouth and passes through the pharynx, which has many tiny openings called pharyngeal slits. A groove called the endostyle makes a slippery substance that traps food particles. The trapped food moves along a groove to the digestive system, while the water leaves the body through a small opening. Both young and adult lancelets can clear their throats if something gets stuck.

Tunicates

Tunicates, such as ascidians, salps, and larvaceans, are special kinds of animals called chordates. They are closely related to vertebrates and lancelets. Almost all tunicates are suspension feeders. This means they catch tiny particles of plankton by filtering seawater through their bodies. Water enters through a special opening called the buccal siphon, helped by tiny hair-like structures called cilia. The water then leaves through another opening after passing through the tunicate's body. To get enough food, a typical tunicate needs to filter about one of its own body volumes of water every second.

Arthropods

Aquatic arthropods, like crustaceans, can feed by filtering. They don’t use hair-like structures called cilia. Instead, they use special body parts to catch food. For example, Mysidaceans live near shorelines and collect tiny particles from the water using a basket-like structure. They are eaten by larger fish like herring, cod, flounder, and striped bass.

Antarctic krill can eat very small plants in the water called phytoplankton, which most animals their size cannot. They use their front legs to form a basket for catching these tiny plants. Other aquatic insects, such as mayfly nymphs, mosquito larvae, and black fly larvae, also filter feed. Some caddisfly larvae make silk nets to catch food from the water. Many barnacles are filter feeders too, using their legs to sift tiny creatures from the water.

Bivalves

Bivalves are water animals with shells made of two parts. Many types, like scallops, clams, oysters, and mussels, eat by filtering tiny bits of food from the water. They take in water and catch small plants and animals on their gills. Then they move the food to their mouths to eat.

Oysters can clean large amounts of water. In the past, the Chesapeake Bay had so many oysters that they could clean all the water in just a few days. Today, it would take longer, but oysters still help by removing harmful substances from the water. Bivalves are important for showing how healthy water is because they stay in one place and are always exposed to the water around them.

Lophophorates

Lophophorates are a group of animals closely related to molluscs. They include brachiopods, bryozoans, and phoronids. These animals have a special organ called the lophophore that helps them eat. The lophophore is made of a ring of ciliated tentacles. Water moves into the lophophore from the sides and leaves from the front.

The lophophore catches tiny food particles, like phytoplankton, and moves them to the animal's mouth. The food then goes through the mouth, down a tube called the pharynx, and into the oesophagus. The stomach digests the food, and nutrients travel through the body to be used. Waste products are released through the body's outer layers.

Sponges

Sponges do not have a real system to move blood. Instead, they create a flow of water to help them get what they need. This water brings gases to their cells and takes away waste. Sponges can move a lot of water. For example, a small sponge called Leuconia about 10 cm tall can pull water in through many tiny canals. The water moves slowly through the sponge so it can catch food easily. Finally, the water flows out through a single opening, helping to push waste away from the sponge.

Cnidarians

The moon jellyfish uses a grid of fibers that moves slowly through the water. This slow motion helps it catch small animals like copepods.

Other filter-feeding animals in this group include corals, sea pens, sea fans, plumose anemones, and Xenia. These animals also have special ways to catch food from the water.

Crinoids

Crinoids, also called feather stars or sea lilies, are special animals called echinoderms. They often have a stalk that helps them stick to the ocean floor, but many can swim when they are young and move around as adults. Crinoids catch their food by letting water flow over their arms, which look like feathers. These arms have tiny parts called tube feet that trap small bits of food and particles from the water.

When crinoids catch food, they move it along special paths to their mouths. Their bodies have a simple way of digesting food, without a true stomach. After digesting, they release waste in small, sticky balls that fall to the ocean floor. Some crinoids have very long, branched arms to catch more food when there isn’t much around.