Breviatea, commonly known as breviate amoebae,
The lineage emerged roughly one billion years ago, at a time when the oxygen content of the Earth's oceans was low, and they thus developed anaerobic lifestyles. Together with Apusomonad, they are the closest relatives of the Opisthokont, a group that includes animals and fungi.
Characteristics
Mitochondrion-related organelles
Mitochondrion-related organelles (MROs) are organelles that evolved from a degradation of ancestral, fully functional
mitochondria. Among Breviatea, MROs are present in
Pygsuia,
Breviata and
Subulatomonas. In the cells of
Pygsuia, for which the complete
transcriptome is known, there is a single smooth MRO that lacks a mitochondrial genome and most components of the electron transport chain. Of the citric acid cycle enzymes, which are present in the mitochondria in other organisms, only two are present in
Pygsuia:
fumarase and succinate dehydrogenase. In contrast,
Lenisia cells contain multiple MROs with
.
Evolution
Breviatea is a
clade of
basal group . They are closely related to the
and the
Opisthokonta supergroup, and together they compose the larger clade
Obazoa, which is the sister group to
Amoebozoa.
Within Breviatea, the four known species are distributed into smaller clades of two species each: one uniting
Breviata with
Subulatomonas, and one uniting
Lenisia with
Pygsuia.
Taxonomy
History
The class Breviatea was created in 2004 by British protozoologist Thomas Cavalier-Smith to group a problematic taxon previously known as
‘Mastigamoeba invertens’. This organism, initially classified in the
Archamoebae within phylum
Amoebozoa, appeared to strongly diverge in
phylogenetic trees based on
ribosomal RNA and had a structure very different from other Archamoebae. Because of these results,
‘M. invertens’ was separated into the order
Breviatida, contained in the monotypic class
Breviatea.
The organism was eventually renamed
Breviata anathema.
A family-level rank for these amoebae,
Breviatidae, was formally described by the same author in 2013.
Classification
There are currently four accepted genera, each containing only one species.
