The genome of the choanoflagellate
Monosiga brevicollis and the origin of metazoans.
These data support the view that all animals are derived from choanoflagellates
, but cannot differentiate between single or multiple origins of multicellularity.
One of the best studied groups of heterotrophic flagellates is the choanoflagellates
Over 600 million years ago, the single-celled choanoflagellates
(Latin for "bearing a collar and a whiptail") branched off from the same ancestor that gave rise to animals.
Hsp70 sequences indicate that choanoflagellates
are closely related to animals.
One end of the choanoflagellate
cell is adorned with a long whip, or flagellum.
Nematostella also has a number of cadherin genes, which, like the choanoflagellate
genes, are most similar to the Flamingo, Fat, and protocadherin subfamilies (Fig.
Differences between the structure of sponge choanocytes and the choanoflagellate
cell, and the fact that many choanocytes are arranged within single chambers in a sponge (Fig.
Other studies suggest that TRPM, along with TRPA and TRPC, has evolved later in the unikont lineage, as it is present in the genomes of the choanoflagellates
Monosiga brevicollis and Salpingosea rosetta, representing the last unicellular ancestor of Metazoa (Mederos y Schnitzler et al.
In the new vision--based on increasingly sophisticated genetic analyses--people and other animals are closer cousins to single-celled choanoflagellates
than to other multicellular organisms.
Recently, integrins and other components of the integrin-mediated adhesion and signalling machinery have been identified in unicellular organisms; such as in the filasterean Capsaspora owczarzaki, a close relative of metazoans and choanoflagellates
By this means it was revealed that all the flagella and cilia in animals including sponges, Mesozoa and choanoflagellates
showed the twoheaded outer arm profile.