The organisms classified as Helkesida commonly have a gliding motility in which the cells glide on their posterior flagellum. They are ancestrally amoeboid bi-flagellates without scales or theca.[2] 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.[4]
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.[5]
Some host species can harbor different helkesid 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]
The initial name for this group, Sainouroidea, had the -oidea suffix for superfamilies, but it was not assigned to any existing classes or orders due to the uncertainty of its phylogenetic position.[5] In a 2018 revision, the class Helkesea and order Helkesida were created as a substitute for this name. Sainouroidea was then 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.[1]
Cladogram of Helkesida, based on a 18S rDNA phylogenetic analysis within a 2018 study.[3] The study names this group "Sainouroidea" due to being published prior to the taxonomic change to Helkesida.[1]
^ abcAdl 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. PMC6492006. PMID30257078.
^ abcdCavalier-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. PMID19523874.
^ abcBass 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. PMID26914587.
^Flavin M, O'Kelly CJ, Nerad TA, Wilkinson G (2000). "Cholamonas cyrtodiopsidis gen. n., sp. n.(Cercomonadida), an endocommensal, mycophagous heterotrophic flagellate with doubled kinetid". Acta Protozoologica. 39 (1): 51–60.
^Sandon H (1924). "Some Protozoa from the Soils and Mosses of Spitsbergen. Results of the Oxford University Expedition to Spitsbergen, No. 27". Zoological Journal of the Linnean Society. 35 (237): 449–475. doi:10.1111/j.1096-3642.1924.tb00051.x.
^Cavalier-Smith T, Lewis R, Chao EE, Oates B, Bass D (2008). "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. PMID18583188.
^Woodcock HM, Lapage G (1915). "Observations on the life-cycle of a new flagellate, Helkesimastix fæcicola, n. g., n. sp.: Together remarks on the question of syngamy in the trypanosomes". Proc. R. Soc. Lond. B. 88 (604): 353–370. doi:10.1098/rspb.1915.0001.
^Hawes RS (1963). "On Rosculus ithacus gen. n., sp. n. (Protozoa, Amoebina), with special reference to its mitosis and phylogenetic relations". Journal of Morphology. 113 (2): 139–149. doi:10.1002/jmor.1051130202. PMID14061990. S2CID40212732.