Bikont

For other uses, see Bikont (disambiguation).

Bikonts Temporal range:
A radiolarian
Scientific classification Edit this classification
Domain:	Eukaryota
(unranked):	Orthokaryotes
(unranked):	Neokaryotes
(unranked):	Bikonta Cavalier-Smith, 1993
Subgroups
Diaphoretickes Excavata Hemimastigophora
Synonyms
Biciliata Cavalier-Smith, 1993 Diaphoretickes Adl et al., 2012 Diphoda Derelle et al., 2015

A bikont ("two flagella") is any of the eukaryotic organisms classified in the group Bikonta. Many single-celled and multi-celled organisms are members of the group, and these, as well as the presumed ancestor, have two flagella.

Enzymes

Another shared trait of bikonts is the fusion of two genes into a single unit: the genes for thymidylate synthase (TS) and dihydrofolate reductase (DHFR) encode a single protein with two functions.

The genes are separately translated in unikonts.

Relationships

Some research suggests that a unikont (a eukaryotic cell with a single flagellum) was the ancestor of opisthokonts (Animals, Fungi, and related forms) and Amoebozoa, and a bikont was the ancestor of Archaeplastida (Plants and relatives), Excavata, Rhizaria, and Chromalveolata. Cavalier-Smith has suggested that Apusozoa, which are typically considered incertae sedis, are in fact bikonts.

Relationships within the bikonts are not yet clear. Cavalier-Smith has grouped the Excavata and Rhizaria into the Cabozoa and the Archaeplastida and Chromalveolata into the Corticata, but at least one other study has suggested that the Rhizaria and Chromalveolata form a clade.

An alternative to the Unikont–Bikont division was suggested by Derelle et al. in 2015, where they proposed the acronyms Opimoda–Diphoda respectively, as substitutes to the older terms. The name Diphoda is formed from the letters of DIscoba and diaPHOretickes (shown in capitals). [suggested singular forms are Opneme-Dipheme respectively]

Cladogram

A "classical" cladogram (data from 2012, 2015) is:

Eukaryotes	Bikonta SAR/HA Supergroup Archaeplastida (inc. land plants) Cryptophyta Haptophyta SAR supergroup Rhizaria Halvaria Heterokont Alveolata Excavata Unikonta

However, a cladogram (data from 2015, 2016) with the root in Excavata is

Eukaryotes	Diphoda (Bikonts) SAR/HA Supergroup Archaeplastida (inc. land plants) Chromista Hacrobia Cryptista Haptista SAR supergroup Rhizaria Halvaria Heterokonta Alveolata Discoba Metamonada? Opimoda (Unikonts) Metamonada? podiates Neolouka Collodictyon Varisulca Amoebozoa Obazoa Apusomonadida Breviata Opisthokonta

The corticates correspond roughly to the bikonts. While Haptophyta, Cryptophyta, Glaucophyta, Rhodophyta, the SAR supergroup and Viridiplantae are usually considered monophyletic, Archaeplastida may be paraphyletic, and the mutual relationships between these phyla are still to be fully resolved.

Recent reconstructions placed Archaeplastida and Hacrobia together in an "HA supergroup" or "AH supergroup", which was a sister clade to the SAR supergroup within the SAR/HA supergroup. However, this seems to have fallen out of favor as the monophyly of hacrobia has come under dispute.

See also

• Corticata

Further reading

• Data related to Bikonta at Wikispecies
• Error creating thumbnail: File missing Media related to at Wikimedia Commons
• Tree of Life Eukaryotes