The cells of cutosean amoebae are surrounded by a continuous thin, somewhat flexible envelope, unique in structure because it is not attached to the cytoplasmic membrane. Below this envelope, they present oval microscales surrounded by a dense matrix. The small scales are not visible under a light microscope.[2] The envelope is penetrated by one or many small pores, which allow subpseudopodia to occasionally protrude from the cell membrane,[3] for a very slow locomotion. Locomoting cells are flattened, oval or round in shape. All of their cells lack cilia or centrosomes,[1] except for the uniciliate swarm cells of the amoeboflagellate Idionectes.[4]
Taxonomy
History
Cutosea is a clade discovered through a 2016 phylogenetic study by Thomas Cavalier-Smith and his coauthors, published in the journal Molecular Phylogenetics and Evolution. It is described as a class-level rank, monotypic as it contains only one order Squamamoebida. Additionally, it is grouped under the monotypic superclass Cutosa. In traditional rank-based classifications, it is grouped within the paraphyleticLobosa, a subphylum of Amoebozoa that also contains Tubulinea and Discosea. Cutosean amoebae present a structurally unique cellular envelope, their distinguishing feature. Their names derive from the Latincutis, meaning 'skin', and squama, meaning 'scale', referencing this envelope.[1]
The Cutosea clade is supported by posterior molecular and morphological studies, and has been accepted as of 2019 by the International Society of Protistologists, which revises the modern cladistic classification of eukaryotes.[3] The first genera to be grouped within Cutosea were Sapocribrum and Squamamoeba, discovered in 2015 and 2013 respectively, and placed in separate families Sapocribridae and Squamamoebidae. A third genus was discovered later in 2018, Armaparvus, which was added to Squamamoebidae.[2] The fourth genus, Idionectes was discovered by Sebastian Hess and Alastair G. B. Simpson in 2019.[5][6]
Classification
Cutosea contains a total of four species, distributed in four monotypic genera:
^ abAdl 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.
^Kudryavtsev, Alexander; Pawlowski, Jan (2013). "Squamamoeba japonica n. g. n sp. (Amoebozoa): a deep-sea amoeba from the Sea of Japan with a novel cell coat structure". Protist. 164 (1): 13–23. doi:10.1016/j.protis.2012.07.003.
^Kang, Seungho; Tice, Alexander K; Spiegel, Frederick W; Silberman, Jeffrey D; Pánek, Tomáš; Čepička, Ivan; Kostka, Martin; Kosakyan, Anush; Alcântara, Daniel M C; Roger, Andrew J; Shadwick, Lora L; Smirnov, Alexey; Kudryavtsev, Alexander; Lahr, Daniel J G; Brown, Matthew W (September 2017). "Between a Pod and a Hard Test: The Deep Evolution of Amoebae". Molecular Biology and Evolution. 34 (9): 2258–2270. doi:10.1093/molbev/msx162. PMC5850466. PMID28505375.
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