Cercomonad Explained

Cercomonads are small amoeboflagellates, widespread in aqueous habitats and common in soils.^[1]

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,^[2] 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.

Classification

Genetic studies place the cercomonads among the Cercozoa,^[3] 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,^[4] while the rest of the family Heteromitidae has been moved to Glissomonadida.^[5] 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.

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

Notes and References

1. Karpov SA, Bass D, Mylnikov AP, Cavalier-Smith T . Molecular phylogeny of Cercomonadidae and kinetid patterns of Cercomonas and Eocercomonas gen. nov. (Cercomonadida, Cercozoa) . Protist . 157 . 2 . 125–58 . June 2006 . 16647880 . 10.1016/j.protis.2006.01.001 .
2. Bass . D.. Howe . A.. Mylnikov . A.. Vickerman . K.. Chao . E.. Edwards Smallbone . J.. Snell . J.. Cabral Jr . J.. Cavalier-Smith . T.. Phylogeny and Classification of Cercomonadida (Protozoa, Cercozoa): Cercomonas, Eocercomonas, Paracercomonas, and Cavernomonas gen. Nov. Protist. 160. 4. 483–521. 2009. 19589724. 10.1016/j.protis.2009.01.004.
3. Bass D, Richards TA, Matthai L, Marsh V, Cavalier-Smith T . DNA evidence for global dispersal and probable endemicity of protozoa . BMC Evol. Biol. . 7 . 162 . 2007 . 17854485 . 2194784 . 10.1186/1471-2148-7-162 . free .
4. Cavalier-Smith . T. . 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 . 2018 . 5756292 . 10.1007/s00709-017-1147-3 . 28875267.
5. Howe . A. T. . Bass . D. . Vickerman . K. . Chao . E. E. . Cavalier-Smith . T. . Phylogeny, taxonomy, and astounding genetic diversity of Glissomonadida ord. nov., the dominant gliding zooflagellates in soil (Protozoa: Cercozoa) . Protist . 160 . 2 . 159–189 . 2009 . 10.1016/j.protis.2008.11.007 . 19324594.