A number of parabasalids and oxymonads are found in
termiteguts, and play an important role in breaking down the
cellulose found in
wood. Some other metamonads are
parasites.
These flagellates are unusual in lacking
mitochondria. Originally they were considered among the most primitive
eukaryotes, diverging from the others before mitochondria appeared. However, they are now known to have lost mitochondria secondarily, and retain both organelles and nuclear genes derived from them. Mitochondrial relics include
hydrogenosomes, which produce
hydrogen, and small structures called
mitosomes.
It now appears the Metamonada are, together with Malawimonas, sister clades of the
Podiata.[3]
All of these groups are united by having
flagella or basal bodies in characteristic groups of four, which are often associated with the
nucleus, forming a structure called a karyomastigont. In addition, the genera Carpediemonas and Trimastix are now known to be close relatives of the retortamonad-diplomonad line and the oxymonads, respectively. Both are free-living and amitochondriate.
Classification
The metamonads were thought to make up part of the
Excavata, a paraphyletic eukaryotic supergroup including flagellates with feeding grooves and their close relatives. Their relationships are uncertain,[4] and they do not always appear together on molecular trees. It is possible that the metamonads as defined here do not form a
monophyletic subgroup.
The following higher level treatment from 2013 is based on works of
Cavalier-Smith[5] with amendments within
Fornicata from Yubukia, Simpson & Leander.[6]
Metamonada were once again proposed to be basal eukaryotes in 2018.[7]
^Cavalier-Smith T (2013). "Early evolution of eukaryote feeding modes, cell structural diversity, and classification of the protozoan phyla Loukozoa, Sulcozoa, and Choanozoa". Eur. J. Protistol. 49 (2): 115–178.
doi:
10.1016/j.ejop.2012.06.001.
PMID23085100.
^Yubukia; Simpson; Leander (2013). "Comprehensive Ultrastructure of Kipferlia bialata Provides Evidence for Character Evolution within the Fornicata (Excavata)". Protist. 164 (3): 423–439.
doi:
10.1016/j.protis.2013.02.002.
PMID23517666.
^Cepicka, Ivan; Hampl, Vladimír; Kulda, Jaroslav (July 2010). "Critical Taxonomic Revision of Parabasalids with Description of one New Genus and three New Species". Protist. 161 (3): 400–433.
doi:
10.1016/j.protis.2009.11.005.
PMID20093080.