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| Sainouroidea | |
|---|---|
 | |
| Different forms of Rosculus vilicus | |
Scientific classification  | |
| Domain: | Eukaryota |
| Clade: | Sar |
| Clade: | Rhizaria |
| Phylum: | Cercozoa |
| Subphylum: | Filosa |
| Infraphylum: | Monadofilosa |
| Superfamily: | Sainouroidea Cavalier-Smith in Cavalier-Smith et al. 2009 |
| Type genus | |
| Sainouron Sandon 1924 | |
| Families | |
| Diversity[1] | |
| 29 species | |
| Synonyms | |
| |
Sainouroidea is a superfamily of microscopic protists belonging to the supergroup Rhizaria, both discovered through molecular phylogenetic analyses. It contains amoeboid flagellates with two flagella. They are either free-living, mostly on fecal matter, or live inside the gut of animals. Among these amoebae, one lineage has independently evolved aggregative multicellularity similarly to slime moulds.[3]
Biology
[edit]Sainouroids commonly have a gliding motility in which the cells glide on their posterior flagellum. They are ancestrally amoeboid bi-flagellates without scales or theca.[4] Unlike most Cercozoa which have tubular mitochondrial cristae, they can also present flat cristae or discoid cristae. They are the only group within Rhizaria that present discoid mitochondrial cristae.[5]
These organisms have an amorphous apical centrosome attached to the nucleus by a rhizoplast. The kinetid arises from 2–4 very short centrioles with dense fibrous roots that attach them to each other and to the nucleus. Their anterior flagellum is reduced to a stub without its 9+2 axoneme. The centrosome also generates numerous microtubules in larger cells. The Golgi apparatus is seen attached to the nuclear envelope and the anterior rhizoplast. They have a microbody attached to the posterior end of the nucleus.[6]
One sainouroid genus, Guttulinopsis, represents an independent lineage in which aggregative multicellularity has evolved to generate "fungi-like" fruiting bodies called sorocarps, similarly to slime moulds such as Dictyostelium.[5]
Ecology
[edit]The sainouroid amoebae are bacterivores that can be free-living, mostly associated to fecal environments, or endozoic, associated to animals.[7] They thrive in aerobic conditions and the microaerophilic gut environment of animals. Rosculus can thrive in anaerobic culture. It is unknown if their preferred habitat is free-living or endozoic.[3]
Some host species can harbor different sainouroid genera and species. One animal can be infected by multiple species simultaneously, and one species can also infect different animal hosts. More sampling of hosts, amoebae and molecular data is needed to better understand the life history and ecology of these protists.[3]
Evolution and systematics
[edit]History
[edit]Sainouroidea was discovered in 2009 as a highly divergent clade within Cercozoa through phylogenetic analyses that used the sequencing of 18S ribosomal RNA from Cholamonas cytrodiopsidis, Sainouron acronematica and Helkesimastix marina. It is a molecularly diverse clade that branches within a group of ancestrally amoeboid bi-flagellates that usually lack an outer cell coat, known as Monadofilosa.[6] A 2016 study revealed a previously unknown wide diversity of Sainouroidea in fecal environments. Previous environmental samplings excluded sequences from Sainouroidea due to their highly divergent 18S rDNA sequences.[7]
The initial name for this group, Sainouroidea, had the -oidea suffix for superfamilies, it was not assigned to any existing orders due to the uncertainty of its phylogenetic position.[6] In a 2018 revision, the order Helkesida were created as a substitute for this name, now also including the family Guttulinopsidae. It was placed in a new class Helkesea, which also included the order Ventricleftida. Superfamily Sainouroidea was modified to only include one of the three helkesid families, Sainouridae. A second superfamily, Helkesimastigoidea, was created to host the remaining two families, Helkesimastigidae and Guttulinopsidae.[8]
Later, in another 2018 revision, order Ventricleftida was transferred to a new subclass named Ventricleftia in class Thecofilosea instead, class Helkesea remained monotypic.[9] A 2018 study described several new genera and species, and used the name Sainouroidea for all three families and new genera.[3] New genera described in that study were later assigned to the families Sainouridae and Guttulinopsidae in 2019 by Adl et al.[4] The name Sainouroidea remains the mostly used name for this whole clade.[3][4][10] Helkesimastigoidea is monophyletic.[3]
Classification
[edit]| Phylogeny of Sainouroidea |
| Cladogram of Sainouroidea, based on a 18S rDNA phylogenetic analysis within a 2018 study.[3] |
Currently, Sainouroidea contains 9 genera and 3 families.[4][3] Additionally, many OTUs found through environmental sequencing may represent undescribed clades.[5][7]
- Superfamily Sainouroidea Cavalier-Smith in Cavalier-Smith et al. 2009
- Family Sainouridae Cavalier-Smith et al. 2008[11] (paraphyletic)
- Acantholus Schuler & Brown in Schuler et al. 2018[3]
- Cholamonas Flavin et al. 2000[3]
- Homocognata Schuler, Silberman & Brown in Schuler et al. 2018[3]
- Sainouron Sandon 1924[3]
- Clade Helkesimastigoidea Cavalier-Smith 2018
- Family Helkesimastigidae Cavalier-Smith in Cavalier-Smith et al. 2009
- Helkesimastix Woodcock & Lapage 1915[3]
- Family Guttulinopsidae Olive 1970
- Guttulinopsis Olive 1901[3]
- Olivorum Schuler, Tice, Silberman & Brown in Schuler et al. 2018[3]
- Puppisaman Schuler & Brown in Schuler et al. 2018[3]
- Rosculus Hawes 1963[3]
- Family Helkesimastigidae Cavalier-Smith in Cavalier-Smith et al. 2009
- Family Sainouridae Cavalier-Smith et al. 2008[11] (paraphyletic)
References
[edit]- ↑ Guiry, M.D. & Guiry, G.M. 2026. AlgaeBase. World-wide electronic publication, University of Galway. https://www.algaebase.org; searched on 5 September 2026.
- ↑ Ruggiero, Michael A.; Gordon, Dennis P.; Orrell, Thomas M.; Bailly, Nicolas; Bourgoin, Thierry; Brusca, Richard C.; Cavalier-Smith, Thomas; Guiry, Michael D.; Kirk, Paul M. (2015-04-29). "A Higher Level Classification of All Living Organisms". PLOS ONE. 10 (4) e0119248. doi:10.1371/journal.pone.0119248. ISSN 1932-6203. PMC 4418965. PMID 25923521.
- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Schuler, Gabriel A.; Tice, Alexander K.; Pearce, Rebecca A.; Foreman, Emily; Stone, Jared; Gammill, Sarah; Willson, John D.; Reading, Chris; Silberman, Jeffrey D.; Brown, Matthew W. (2018-12-01). "Phylogeny and Classification of Novel Diversity in Sainouroidea (Cercozoa, Rhizaria) Sheds Light on a Highly Diverse and Divergent Clade". Protist. 169 (6): 853–874. doi:10.1016/j.protis.2018.08.002. ISSN 1434-4610.
- 1 2 3 4 Adl SM, Bass D, Lane CE, Lukeš J, Schoch CL, Smirnov A, Agatha S, Berney C, Brown MW, Burki F, Cárdenas P, Čepička I, Chistyakova L, del Campo J, Dunthorn M, Edvardsen B, Eglit Y, Guillou L, Hampl V, Heiss AA, Hoppenrath M, James TY, Karnkowska A, Karpov S, Kim E, Kolisko M, Kudryavtsev A, Lahr DJG, Lara E, Le Gall L, Lynn DH, Mann DG, Massana R, Mitchell EAD, Morrow C, Park JS, Pawlowski JW, Powell MJ, Richter DJ, Rueckert S, Shadwick L, Shimano S, Spiegel FW, Torruella G, Youssef N, Zlatogursky V, Zhang Q (2019). "Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes". Journal of Eukaryotic Microbiology. 66 (1): 4–119. doi:10.1111/jeu.12691. PMC 6492006. PMID 30257078.
- 1 2 3 Brown MW, Kolisko M, Silberman JD, Roger AJ (2012). "Aggregative Multicellularity Evolved Independently in the Eukaryotic Supergroup Rhizaria". Current Biology. 22 (12): 1123–1127. doi:10.1016/j.cub.2012.04.021. PMID 22608512. S2CID 17510471.
- 1 2 3 Cavalier-Smith T, Lewis R, Chao EE, Oates B, Bass D (2009). "Helkesimastix marina n. sp. (Cercozoa: Sainouroidea superfam. n.) a Gliding Zooflagellate of Novel Ultrastructure and Unusual Ciliary Behaviour". Protist. 160 (3): 452–479. doi:10.1016/j.protis.2009.03.003. PMID 19523874.
- 1 2 3 Bass D, Silberman JD, Brown MW, Pearce RA, Tice AK, Jousset A, Geisen S, Hartikainen H (2016). "Coprophilic amoebae and flagellates, including Guttulinopsis, Rosculus and Helkesimastix, characterise a divergent and diverse rhizarian radiation and contribute to a large diversity of faecal-associated protists". Environ Microbiol. 18 (5): 1604–1619. doi:10.1111/1462-2920.13235. PMID 26914587.
- ↑ Cavalier-Smith, Thomas (2018-01-01). "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. ISSN 1615-6102. PMC 5756292. PMID 28875267.
- ↑ Cavalier-Smith, Thomas; Chao, Ema E.; Lewis, Rhodri (2018-09-01). "Multigene phylogeny and cell evolution of chromist infrakingdom Rhizaria: contrasting cell organisation of sister phyla Cercozoa and Retaria". Protoplasma. 255 (5): 1517–1574. doi:10.1007/s00709-018-1241-1. ISSN 1615-6102. PMC 6133090. PMID 29666938.
- ↑ Lax, Gordon; Cooney, Elizabeth C.; Zlatogursky, Vasily; Mtawali, Mahara; Okamoto, Noriko; Jacko-Reynolds, Victoria K. L.; Bjornson, Saelin; Holt, Corey; Hurdeal, Vedprakash G.; Giannotti, Daniele; Keeling, Patrick J. (2026-01-30). "Phylogenomic tree of Cercozoa based on single-cell transcriptomes from 100 uncultured cells". BMC Biology. 24 (1): 55. doi:10.1186/s12915-026-02536-4. ISSN 1741-7007. PMC 12930898. PMID 41618358.
- ↑ Cavalier-Smith, Thomas; Lewis, Rhodri; Chao, Ema E.; Oates, Brian; Bass, David (2008-10-21). "Morphology and Phylogeny of Sainouron acronematica sp. n. and the Ultrastructural Unity of Cercozoa". Protist. 159 (4): 591–620. doi:10.1016/j.protis.2008.04.002. ISSN 1434-4610.