Choanoflagellate Totally Explained

Everything about The Choanoflagellate totally explained

The choanoflagellates are a group of occasionally colonial flagellate protozoa. They are considered to be the closest living relatives of the animals; the last unicellular ancestors of animals are thought to have resembled modern choanoflagellates.

Appearance and ecology

Choanoflagellates resemble the individual cells of sponges: each choanoflagellate has a single flagellum, surrounded by a ring of actin-filled protrusions called microvilli, forming a cylindrical or conical collar (choanos in Greek). The flagellum draws water through the collar, and bacteria and detrital particles are captured by the microvilli and ingested. Even today they're important in the carbon cycle and microbial food web.

Colonial behaviour

Most choanoflagellates are sessile, with a stalk opposite the flagellum. A number of species such as those in the genus Proterospongia may form simple colonies, usually taking the form of a cluster of cells on a single stalk, but often forming planktonic clumps that resemble a miniature cluster of grapes in which each cell in the colony is flagellated. Many choanoflagellates build complex basket-shaped "houses" called lorica, from several silica strips cemented together. This multicellularity is achieved in a very different way to the animals.

Abundance and diversity

There are over 125 extant species of choanoflagellates. They are distributed ...

Comparison and relationship with other taxa

The choanocytes (also known as "collared cells") of sponges (considered the most basal metazoa) have the same basic structure as choanoflagellates. Collared cells are occasionally found in a few other animal groups, such as flatworms.
Genome sequencing shows that among living organisms, the choanoflagellates are most closely related to animals.
The last common ancestor of animals AND choanoflagellates was unicellular, perhaps forming simple colonies; in contrast, the last common ancestor of all animals was a relatively complex multicellular organism, with differentiated tissues, a definite "body plan", and complex embryonic development (including gastrulation). The timing of the splitting of these lineages is difficult to constrain, but was probably in the late Precambrian, >. The genome of choanoflagellates, with 41.6 million base pairs, is similar in size to filamentous fungi and other free-living unicellular eukaryotes, but far smaller than that of typical animals.Further Information

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