Choanoflagellate

Tiny living things live in the water.

They have a little tail. This tail helps them swim. It also moves the water. This moves food toward them. They catch food with a collar. This collar looks like a funnel.

These tiny things are like small cousins to animals. Some live all alone. Others live in groups. These groups look like tiny grapes.

They live in oceans and lakes all over the world.

Choanoflagellates are tiny living things found in water all over the world. They live in oceans and lakes. Some live alone, but others live in groups called colonies.

These groups can look like small clusters of grapes.

These tiny cells are the closest living relatives to animals. This means they are like very distant cousins to us.

Scientists study them to learn how animals first began. They look a lot like certain cells in sponges. Sponges are very simple animals.

Each cell has a special part called a flagellum. This is a little tail that moves. The tail is surrounded by a ring of tiny parts called microvilli. Together, these parts make a collar that looks like a funnel.

When the flagellum moves, it creates a water current. This current pulls water through the funnel. The collar then traps food like bacteria. The cell eats this food to grow. Some species even build tiny houses called a lorica. They make these from bits of silica, which is a type of glass.

Choanoflagellates are tiny, single-celled living things found in water everywhere. They live in oceans, lakes, and even under Antarctic ice sheets.

Some live alone, but others form groups called colonies. These colonies can look like small clusters of grapes.

Scientists find them very important for the carbon cycle. They eat bacteria and help move energy through the food web. This makes them a key part of life in the water.

Each cell has a special way it works to eat and move. A single tail called a flagellum sits in the middle. This tail is surrounded by a ring of tiny parts called microvilli. Together, they form a collar that looks like a funnel.

When the flagellum moves, it creates a water current. This current pulls water through the funnel collar. The collar then traps food like bacteria and tiny bits of debris. The cell then swallows this food to stay alive.

These tiny creatures are the closest living relatives to animals. This makes them a great model for studying how animals began.

A French biologist named Félix Dujardin noticed this in 1841. He saw that their cells looked like choanocytes in sponges. Sponges are very simple animals. Many studies since the 1990s have proven this close family link. They use genetic tests to show that choanoflagellates and animals share a common history.

There are over 125 known species of choanoflagellates today. They can be found in the Arctic or the tropics.

Some species, like Diaphanoeca grandis, live in North America, Europe, and Australia. Scientists have different ideas about how old this group is. One study from 2017 says they split from other groups 786.62 million years ago. However, a 2021 study suggests they appeared 422.78 million years ago. These numbers help us understand the deep history of life.

Choanoflagellates show us how simple life can become complex. Some species even build tiny, basket-shaped houses called a lorica.

They make these houses using strips of silica, which is like glass. This is a very special skill for such small cells. We can see how their parts are similar to much larger things. For example, the way they manage calcium is like a human sperm cell. Studying these small cells helps us understand the very first animals.

Choanoflagellates are a diverse group of single-celled and colonial organisms. They are eukaryotes, meaning their cells contain a nucleus. These tiny creatures live in almost every aquatic environment on Earth. You can find them in oceans, brackish water, and freshwater. They live in places ranging from the tropical heat to the freezing Antarctic ice sheets.

Scientists study them because they are the closest living relatives to animals. By looking at them, researchers can try to reconstruct the very first animal ancestor. This makes them a vital link in understanding how complex life began.

Each choanoflagellate has a very specific body structure. A single, whip-like tail called a flagellum sits at the top of the cell. This flagellum is surrounded by a ring of tiny, finger-like protrusions called microvilli. These microvilli are filled with actin, a type of protein. Together, the flagellum and the microvilli form a funnel-shaped structure called a collar.

This unique shape is how the name "choanoflagellate" is derived, using the Greek word for funnel. The internal parts are also organized in a consistent way. A flagellar basal body sits at the base of the flagellum. A second, non-flagellar basal body is located at a right angle to the first one. The nucleus is usually found in the center or toward the top of the cell.

The collar is not just for show; it is a highly efficient feeding tool. When the flagellum moves, it creates a steady water current. This current pulls water directly through the microvilli collar. As the water passes through, it carries bacteria and organic debris, known as detritus. The microvilli trap these food particles against the collar. The cell then engulfs the trapped food.

This movement also helps the cell move through the water. Unlike many other flagellated cells that are pulled by their tails, choanoflagellates act as "pushers." The flagellum pushes the cell forward through the water column.

Choanoflagellates can live as solitary individuals or in groups called colonies. Some species, like Proterospongia, form simple clumps that look like tiny clusters of grapes.

Other species, such as Barroeca monosierra, create complex spheres. These spheres contain a branched network of an extracellular matrix. This matrix provides a home for a microbiome of symbiotic bacteria. Some species are sessile, meaning they stay attached to a surface. They might use a thin stalk called a pedicel or a protective covering called a periplast to stay in place. In moving organisms, the periplast may increase drag to help with feeding efficiency.

Some specialized members of this group, known as Acanthoecids, build tiny structures called a lorica. A lorica is a basket-shaped house made of silica strips. These strips are a biocomposite made of silica and protein. The cell creates these strips internally and then secretes them to the surface.

In some species, tentacles help assemble the strips into a full lorica. In others, the strips gather in an arrangement below the collar. This process requires the cell to concentrate silicic acid using special silicon transporter (SiT) proteins. Interestingly, these genes likely arrived through horizontal gene transfer from a different group called Stramenopiles.

The history of studying these organisms goes back quite far. In 1841, a French biologist named Félix Dujardin noticed something important. He saw that the cells of choanoflagellates looked very similar to choanocytes. Choanocytes are specialized "collared cells" found in sponges. Because sponges are among the most basic animals, this suggested a deep connection. Since the 1990s, many genetic studies have confirmed this relationship. Scientists have analyzed mitochondrial genomes and protein-coding genes to prove that choanoflagellates are an outgroup to the animal kingdom.

This means they are the closest unicellular relatives to all animals.

Determining exactly when these lineages split is a challenge for scientists. One study from 2017 suggested the divergence of the crown group happened 786.62 million years ago. However, a more recent study from 2021 placed the appearance of crown group craspedids at 422.78 million years ago. Regardless of the exact date, these organisms play a massive role in the global carbon cycle. They eat bacteria and viruses, which moves carbon up the food web to larger organisms. They act as a bridge between tiny microbes and the larger animals that inhabit our waters.