Bikont

For an explanation of very similar terms, see Corticata.

Bikonts
File:Aulacanthas 01.jpg
A radiolarian
Scientific classification
Domain:	Eukaryota
(unranked):	Bikonta Cavalier-Smith, 1993
Subgroups
Apusozoa Rhizaria Excavata Archaeplastida Chromalveolata
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 members of the group, and 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.

Cladogram

An up to date "classical" cladogram is

Eukaryote	Unikonta Bikonta Excavata Chromalveolata (+ Archaeplastida) SAR supergroup Halvaria Heterokont Alveolata Rhizaria Haptophyta Cryptophyta Archaeplastida

However, an even more up-to date cladogram with the root in Excavata is

Eukaryotes	Euglenozoa Percolozoa Tsukubamonadea Jakobea Metamonada corticata Archaeplastida Chromista Harosa Rhizaria Halvaria Heterokonta Alveolata Hacrobia Haptista Cryptista podiates Amoebozoa Obazoa Breviata Apusomonadida Opisthokont Neolouka Collodictyon Varisulca

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 relationship between these phyla are still to be fully resolved.

Further reading

• Tree of Life Eukaryotes