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What are Choanoflagellates?

Choanoflagellates are fascinating single-celled organisms, often hailed as the closest living relatives of animals. Resembling tiny, aquatic suns with a whip-like tail, they play a crucial role in understanding the evolution of multicellular life. Their study could unlock secrets of our own biological ancestry. Curious about how these microscopic marvels bridge the gap between single-celled and complex life? Let's dive deeper.
Michael Anissimov
Michael Anissimov
Michael Anissimov
Michael Anissimov

The choanoflagellates (meaning "collared organism with a tail") are thought to be similar to the unicellular organism from which all animals evolved, and the closest living unicellular relative to animals. Choanoflagellates are a type of protozoa, meaning a unicellular eukaryote (complex-celled organism), in contrast to other unicellular organisms such as bacteria and archaea. Like many other microbes, choanoflagellates form colonies, which may have been the precursors of the first multicelullar organisms.

Most choanoflagellates are sessile, meaning they stay in one place, fastened to the ocean floor with a stalk. The flagellum whips rapidly, driving water upwards. This flagella is surrounded by microvilli that make up the "collar" that gives the microbe its name. As the flagellum propels upwards to create a suction current, causing bits of food to get stuck to the microvilli. This strategy is called filter feeding, and it is also used by baleen whales, krill, sponges, and other marine organisms. The cell body of the choanoflagellate is also covered by a shield called a theca.

Like many other microorganisms, choanoflagellates are ubiquitous in aquatic environments. They have even been found 100 m (328 ft) below Antarctic ice sheets.

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Frog

The genome of the choanoflagellate has been sequenced, and subsequent analysis has shown that they are closely related to animals. In their behavior, choanoflagellates are among the most complex of protozoa. They even build small silica "houses" called lorica (meaning "body armor"). For further evidence of the close relationship between choanoflagellates and the animals, we see that there are specialized cells in sponges called choanocytes ("collared cells") which bear a great resemblance to choanoflagellates. Choanocytes can also be found in nematodes.

Choanoflagellates are a variety of nanoplankton, referring to the smallest (single-celled) form of organisms in the sea. As such, they are consumed by a variety of larger organisms, including krill and many others. When a choanoflagellate dies, it quickly becomes dislodged from the ocean floor, floating around until it is consumed.

Michael Anissimov
Michael Anissimov

Michael is a longtime AllTheScience contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

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Michael Anissimov
Michael Anissimov

Michael is a longtime AllTheScience contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

Learn more...

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