Retortamonad

{{Short description|Group of flagellates}}

{{Taxobox

| image = Metamonada retortamonas hexamita giardia.svg

| image_caption = Retortamonas (Retortamonadida), on left; Hexamita, on center, and Giardia, on right (both Diplomonadida)

| domain = Eukaryota

| unranked_regnum = Excavata

| phylum = Metamonada

| ordo = Retortamonadida

| subdivision_ranks = Genera

| subdivision =

Retortamonas

Chilomastix

}}

The retortamonads are a small group of flagellates, most commonly found in the intestines of animals as commensals, although a free-living species called the Chilomastix cuspidata exists. They are grouped under the taxon Archezoa.{{cite journal|last1=Silberman|first1=Jeffrey|last2=Simpson|first2=Alastair|last3=Kula|first3=Jaroslav|title=Retortamonad Flagellates are Closely Related to Diplomonads— Implications for the History of Mitochondrial Function in Eukaryote Evolution|journal=Molecular Biology and Evolution|date=31 January 2002|volume=19|issue=5|pages=777–786|pmid=11961110|doi=10.1093/oxfordjournals.molbev.a004135|doi-access=free}} They are usually around 5-20 μm in length, and all of their small subunit ribosomal RNA gene sequences are very similar to each other. There are two genera: Retortamonas with two flagella, and Chilomastix with four. In both cases there are four basal bodies anterior to a prominent feeding groove, and one flagellum is directed back through the cell, emerging from the groove.

The retortamonads lack mitochondria, golgi apparatus, dictyosomes, and peroxisomes. They are close relatives of the diplomonads,{{cite journal |vauthors=Simpson AG, Roger AJ, Silberman JD, etal |title=Evolutionary history of "early-diverging" eukaryotes: the excavate taxon Carpediemonas is a close relative of Giardia |journal=Mol. Biol. Evol. |volume=19 |issue=10 |pages=1782–91 |date=October 2002 |pmid=12270904 |doi= 10.1093/oxfordjournals.molbev.a004000|doi-access=free }} and are placed among the metamonads along with them. Due to the abundant phylogenetic similarities between the two flagellates, since diplomonads do not ancestrally lack mitochondrion, this suggests that retortamonads are also secondarily amitochondriate.