Cercomonad

Cercomonads are small amoeboflagellates,^[2] widespread in aqueous habitats and common in soils.^[3]

Cercomonads
Cercomonas sp
Scientific classification
Domain:	Eukaryota
Clade:	Diaphoretickes
Clade:	SAR
Phylum:	Cercozoa
Class:	Sarcomonadea
Order:	Cercomonadida Poche 1913, emend. Vickerman 1983, emend. Mylnikov 1986, emend. Karpov et al. 2006; emend Howe et al. 2009; emend Cavalier-Smith 2012[1]
Family:	Cercomonadidae Kent 1880, emend. Mylnikov and Karpov 2004[2]
Genera[1]
Cavernomonas Cercomonas Eocercomonas Filomonas Neocercomonas
Synonyms[1]
Cercobodonidae Hollande 1942

Characteristics

The cells are generally around 10 μm in length, without any shell or covering. They produce filose pseudopods to capture bacteria, but do not use them for locomotion, which usually takes place by gliding along surfaces.

Most members have two flagella,^[4] one directed forward and one trailing under the cell, inserted at right angles near its anterior. The nucleus is connected to the flagellar bases and accompanied by a characteristic paranuclear body.

Representation of a cercomonad

1. Anterior flagellum
2. Microtubular bands
3. Fibrillar rootlet
4. Golgi apparatus; modifies proteins and sends them out of the cell
5. Microtubule cone
6. Nucleus
7. Nucleolus
8. Endoplasmic reticulum, the transport network for molecules going to specific parts of the cell
9. Extrusome
10. Contractile vacuole, regulates the quantity of water inside a cell
11. Dense granule
12. Mitochondrion, creates ATP (energy) for the cell, tubular cristae
13. Food vacuole
14. Prey (bacteria)
15. Lysosome, holds enzymes
16. Posterior flagellum

Classification

Genetic studies place the cercomonads among the Cercozoa,^[5] a diverse group of amoeboid and flagellate protozoans. They are divided into two families.

• The Heteromitidae tend to be relatively rigid, and produce only temporary pseudopods.
• The Cercomonadidae are more plastic, and when food supplies are plentiful may become amoeboid and even multinucleate.

The classification of genera and species continues to undergo revision. Some genera have been merged, like Cercomonas and Cercobodo. Others like Helkesimastix, Sainouron and Cholamonas have been moved to Helkesida,^[6] while the rest of the family Heteromitidae has been moved to Glissomonadida.^[7] Most recently, the family Paracercomonadidae, previously included in this order, has been separated into its own order Paracercomonadida. This change has made Cercomonadidae the only existing family of cercomonads.^[1][8]

• Cavernomonas Vickerman 2009
• Cercomonas Dujardin 1841 emend. Karpov et al. 2006 non emend. Ekelund et al. 2004 [Cercobodo Krassilstschick 1886; Cercomastix Lemmermann 1913; Dimastigamoeba Blochmann 1894; ?Mukdeniamonas Skwortzov 1960; ?Changia Skwortzov 1960 non Sun 1924; ?Reptomonas Kent 1880; Dimorpha Klebs 1892 non Gruber 1882]
• Eocercomonas Karpov et al. 2006
• Filomonas Cavalier-Smith & Karpov 2012
• Neocercomonas Ekelund, Daugbjerg & Fredslund 2004

References

1. Sina M. Adl; David Bass; Christopher E. Lane; et al. (1 January 2019). "Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes". Journal of Eukaryotic Microbiology. 66 (1): 4–119. doi:10.1111/JEU.12691. ISSN 1066-5234. PMC 6492006. PMID 30257078. Wikidata Q57086550.
2. Alexander P. Myl'nikov; Serguei A. Karpov (2004). "Review of diversity and taxonomy of cercomonads" (PDF). Protistology. 3 (4): 201–217. ISSN 1680-0826. Wikidata Q124459772.
3. Karpov SA, Bass D, Mylnikov AP, Cavalier-Smith T (June 2006). "Molecular phylogeny of Cercomonadidae and kinetid patterns of Cercomonas and Eocercomonas gen. nov. (Cercomonadida, Cercozoa)". Protist. 157 (2): 125–58. doi:10.1016/j.protis.2006.01.001. PMID 16647880.
4. Bass, D.; Howe, A.; Mylnikov, A.; Vickerman, K.; Chao, E.; Edwards Smallbone, J.; Snell, J.; Cabral Jr, J.; Cavalier-Smith, T. (2009). "Phylogeny and Classification of Cercomonadida (Protozoa, Cercozoa): Cercomonas, Eocercomonas, Paracercomonas, and Cavernomonas gen. Nov". Protist. 160 (4): 483–521. doi:10.1016/j.protis.2009.01.004. PMID 19589724.
5. Bass D, Richards TA, Matthai L, Marsh V, Cavalier-Smith T (2007). "DNA evidence for global dispersal and probable endemicity of protozoa". BMC Evol. Biol. 7: 162. doi:10.1186/1471-2148-7-162. PMC 2194784. PMID 17854485.
6. Cavalier-Smith, T. (2018). "Kingdom Chromista and its eight phyla: a new synthesis emphasising periplastid protein targeting, cytoskeletal and periplastid evolution, and ancient divergences". Protoplasma. 255 (1): 297–357. doi:10.1007/s00709-017-1147-3. PMC 5756292. PMID 28875267.
7. Howe, A. T.; Bass, D.; Vickerman, K.; Chao, E. E.; Cavalier-Smith, T. (2009). "Phylogeny, taxonomy, and astounding genetic diversity of Glissomonadida ord. nov., the dominant gliding zooflagellates in soil (Protozoa: Cercozoa)". Protist. 160 (2): 159–189. doi:10.1016/j.protis.2008.11.007. PMID 19324594.
8. Thomas Cavalier-Smith; Ema E-Yung Chao; Rhodri Lewis (17 April 2018). "Multigene phylogeny and cell evolution of chromist infrakingdom Rhizaria: contrasting cel organisation of sister phyla Cercozoa and Retaria". Protoplasma. doi:10.1007/S00709-018-1241-1. ISSN 0033-183X. PMC 6133090. PMID 29666938. Wikidata Q53073157.