Filter feeder

Filter feeders are special kinds of aquatic animals that get their food by eating tiny bits of organic matter, particles, or small living things like bacteria, microalgae, and zooplanktons that float in the water. They have special organs that act like filters, trapping these small pieces of food as water passes through. This unique way of eating helps them gather nutrients from their environment.

These animals play a very important role in keeping water clean. By eating and gathering together bits of organic material, they help remove extra nutrients such as nitrogen and phosphate from the water. This makes them important for balancing the health of water bodies.

Filter feeders come in many different forms and live in many different places. Some stay in one spot their whole lives, while others float or swim through the water. They include animals from many groups, such as sponges, jellyfish, corals, krill, clams, oysters, and even large animals like baleen whales and manta rays. Even some water birds, like flamingos, act as filter feeders when they search for food in the water.

Vertebrates

Fish

Most forage fish are filter feeders. For example, the Atlantic menhaden, a type of herring, lives on plankton caught in midwater. Adult menhaden can filter up to four gallons of water a minute and play an important role in clarifying ocean water. They also help control the dangerous red tide.

Some cartilaginous fishes are also filter feeders. The whale shark sucks in water and traps tiny animals against special structures in its gills. The megamouth shark and basking shark also filter small creatures from large amounts of water. Manta rays feed on eggs and tiny animals when fish spawn.

Baleen whales

Baleen whales are special whales with plates in their mouths that act like filters. They use these plates to catch tiny animals like krill from the water. These whales swim through groups of small creatures and use their baleen plates to trap food while letting water pass through. Their baleen plates are made of a material similar to human hair and have fine hairs that help trap tiny food. Different types of baleen whales have different ways of feeding, but they all rely on their baleen to catch their food.

Birds

Flamingos are birds that filter-feed on tiny shrimp. Their beaks are specially shaped to separate mud and silt from their food. They use hairy structures 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 has been thought to be filter-feeders because of their long, slender teeth. However, only Pterodaustro had a real way to pump water through its beak to trap food. Other types in this group probably used their teeth to catch food in a different way.

Boreopterids may have used their long, slender teeth to trap small fish, but they likely did not have the same pumping ability as Pterodaustro.

Marine reptiles

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

Lancelets

Lancelets (subphylum Cephalochordata) are fish-like chordates closely related to vertebrates. They live on the seafloor, burrowing into sandy areas. Lancelets are filter feeders, meaning they eat 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, meaning 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, are animals that can feed by filtering. They don’t use hair-like structures called cilia, unlike some other filter feeders. Instead, they use special parts of their bodies 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 are special because they can eat very small plants in the water called phytoplankton, which most animals their size cannot. They use their front legs to form an effective 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 that have two-part shells. 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 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 much longer, but oysters still help by removing harmful substances from the water. Bivalves are also important for showing how healthy water is, because they live 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, which are small plants that can make their own food using sunlight, and moves them to the animal's mouth. The food then goes through the mouth, down a muscular 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 don't have a real system to move blood. Instead, they create a flow of water that helps 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 means that small animals like copepods cannot escape its reach.

Other filter-feeding animals in this group include corals, sea pens, sea fans, plumose anemones, and Xenia. These animals also use 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.