For both choanoflagellate
species and all other metazoan phyla, we did not find any HcM gene (Table AI).
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
. Although many groups are little known, it seems clear that the Antarctica ocean is one of the marine areas with the highest levels of endemism.
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.
Monosiga ovata is the choanoflagellate
species that's just been approved for NHGRI sequencing.
In the case of the Metazoa, one such outgroup that has been examined is the choanoflagellates
, which are single-celled protists hypothesized to be closely related to metazoan taxa.
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.
Immediately after being plated, the dissociated tissues consisted of unattached rounded masses of various sizes, some of which could be identified by their collars and flagella as parts of choanoflagellate
"Biologists for decades believed the existing theory was a no-brainer, as sponge choanocytes look so much like single-celled choanoflagellates
-- the organism considered to be the closest living relatives of the animals," she said.
G protein-coupled receptors exist in eukaryotes, including yeast, choanoflagellates
, and animals .
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.