The kathablepharids or katablepharids (from Greek kata 'downwards', and blepharis 'eyelash') are a group of heterotrophic flagellates closely related to cryptomonads. First described by Heinrich Leonhards Skuja in 1939, kathablepharids were named after the genus Kathablepharis. This genus is corrected to Katablepharis under botanical nomenclature, but the original spelling is maintained under zoological nomenclature. They are single-celled protists with two anteriorly directed flagella, an anterior cytostome for ingesting eukaryotic prey, and a sheath that covers the cell membrane. They have extrusomes known as ejectisomes, as well as tubular mitochondrial cristae.
| Katablepharid | |
|---|---|
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| Light (above) and transmission electron (below) micrographs of Roombia truncata | |
Scientific classification 
| |
| Domain: | Eukaryota |
| Clade: | Diaphoretickes |
| Phylum: | Cryptista |
| Subphylum: | Rollomonadia |
| Superclass: | Leucocrypta Cavalier-Smith 2004 stat. nov. 2015[4] |
| Class: | Leucocryptea Cavalier-Smith 2004[3] |
| Order: | Kathablepharidida Okamoto & Inouye 2005[2] |
| Family: | Kathablepharididae Vørs 1992 emend. Clay & Kugrens 1999[1] |
| Genus | |
| Synonyms | |
Description edit
Morphology edit
Katablepharids are flagellates, unicellular protists capable of swimming freely by using two hairless flagella inserted subapically or medially in the cell. The flagella are both projected forward (anteriorly), or only one flagellum is projected while the other trails. Their cell membrane is thickened by a sheath composed of two layers containing lamellae. The sheath also encases the flagella. Each cell has a nucleus in a central position, a Golgi apparatus in the anterior region, and a food vacuole in the posterior region. Their mitochondria have tubular cristae. Near the kinetosomes they have extrusomes known as 'ejectisomes' of various sizes, each composed of a single coiled ribbon or 'scroll', unlike cryptomonads which have ejectisomes composed of two scrolls.[1][7]
Nutrition edit
These flagellates feed by ingesting other eukaryotes through a cytostome supported by bands of longitudinal microtubules.[7] One species, Kathablepharis hyalurus, has secondarily lost the cytostome.[8] The species Hatena arenicola has a unique life history in comparison: it feeds on Nephroselmis algae, temporarily retains their chloroplasts, enlarges them, and utilizes them for photosynthesis, which allows it to divide and reproduce. This process is known as kleptoplasty.[9]
Systematics edit
Taxonomic history edit
The botanist Heinrich Leonhards Skuja in 1939 described the family Kathablepharidaceae to accommodate colourless flagellates that had two divergent flagella and a longitudinal groove.[5] He included four genera in this family: Kathablepharis, Leucocryptos, Cryptaulax and Phyllomitus.[10] He considered katablepharids as closely related to cryptomonads, and placed them in class Cryptophyceae on the basis of morphological features seen through light microscopy.[11]
In 1992, the protozoologist Naja Vørs created the zoological variant of the family, Kathablepharidae and corrected the botanical variant as Katablepharidaceae,[a] redefined to only include three genera: Katablepharis, Leucocryptos and Platychilomonas.[10] However, she did not assign this family to any higher taxon, and instead treated it as incertae sedis protists, thereby removing them from Cryptophyceae.[13]
An alternative to Vørs' classification was proposed by the protozoologist Thomas Cavalier-Smith in 1993. Through observations of a single species Kathablepharis ovalis, he classified katablepharids as part of the phylum Opalozoa, on the basis of tubular mitochondrial cristae and the absence of ejectisomes that are characteristic of cryptomonads. He erected a new class Cyathobodonea and placed Kathablepharis and Leucocryptos in a new order Kathablepharida, defined by two anterior flagella encased by a surface sheath, lack of cytopharynx, and an anterior cytostome supported by four bands of microtubules.[14][15] The phylum Opalozoa was highly non-monophyletic, and in 1997 Cavalier-Smith separated katablepharids into a new phylum Neomonada which was another broad non-monophyletic assemblage. Katablepharids were placed in a new subphylum Isomita which also contained Telonemea.[16] Because this scheme was based on the observations on a single species K. ovalis, it was not considered valid.[13]
In 1999, Brec Clay and Paul Kugrens reviewed the systematics of katablepharids and rejected Cavalier-Smith's classification. Instead, they adopted Vørs' family, corrected the zoological spelling to Kathablepharididae, emended the diagnosis to include only Katablepharis and Leucocryptos, and postponed any higher classification until molecular phylogenetics could resolve their true placement.[1]
Eventually, molecular data and electron microscopy studies revealed cryptophytes and katablepharids to be related. In 2004, Cavalier-Smith included both group as subphyla under the phylum Cryptista. For katablepharids, he proposed a new class Leucocryptea and subphylum Leucocrypta, named after Leucocryptos.[17] The following year, Noriko Okamoto and Isao Inouye interpreted the molecular and morphological gap between the two groups sufficient to propose them as two separate phyla. They also argued that the treatment of both groups as divisions (=botanical phylum) agrees with the widely accepted system where Cryptophyta is a division. They described higher taxa for both nomenclature codes: phylum Kathablepharida, class Kathablepharidea and order Kathablepharidida under zoological nomenclature, and division Katablepharidophyta, class Katablepharidophyceae and order Katablepharidales under botanical nomenclature.[18][a] In the following years, two new genera of katablepharids were described: Hatena in 2006[19] and Roombia in 2009.[20]
Following his own classification, Cavalier-Smith continued considering both groups as members of phylum Cryptista. In 2015, he lowered Leucocrypta to a superclass included within the subphylum Rollomonadia (equivalent to Cryptophyta), along with cryptomonads (under the name of Cryptomonada), and added additional subphyla Palpitia and Corbihelia to the phylum.[21] As of 2024, katablepharids are generally accepted as a subgroup of the Cryptista or Cryptophyta, instead of an independent phylum or division, together with cryptomonads.[7][22]
Classification edit
There are five accepted genera of katablepharids:[7]
- Hatena Okamoto & Inouye 2006[19]
- Kathablepharis/Katablepharis[a] Skuja 1939
- Leucocryptos Butcher 1967
- Platychilomonas Larsen & Patterson 1990
- Roombia Okamoto, Chantangsi, Horák, Leander & Keeling 2009[20]
Evolution edit
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| Relationships between katablepharids and closely related protists.[23][24] Hacrobian taxa marked with asterisks. |
Besides the known katablepharid diversity, dozens of environmental DNA sequences (both freshwater and marine) seem to represent further katablepharids which have not been cultured or formally described. Through molecular phylogenetic analyses, they are consistently recovered as the sister clade to cryptomonads, an assemblage of flagellates containing the phagotrophic goniomonads and the photosynthetic cryptophytes. Initially, both groups were placed in the Hacrobia, a tentative group that also contained haptophytes, centrohelids, biliphytes and telonemids.[20][25] However, the Hacrobia hypothesis was later disproven. Instead, haptophytes and centrohelids belong to the phylum Haptista, while cryptomonads and katablepharids remain as sister groups within the phylum Cryptista together with Palpitomonas.[7] Haptista is more closely related to the TSAR clade, which includes telonemids, while Cryptista is more closely related to the Archaeplastida clade, which includes red algae, green algae, plants, glaucophytes and biliphytes.[26][23][24]
Within katablepharids, Roombia is the earliest branching genus, followed by Hatena. This genus is in turn the sister group to the remaining genera: Leucocryptos and Katablepharis. The fifth genus, Platychilomonas, is absent in all phylogenetic analyses due to lack of molecular data.[27]
Notes edit
- ^ a b c According to the International Code of Botanical Nomenclature (ICBN) the spelling of Kathablepharis is incorrect and modified to Katablepharis (from Greek kata 'downwards', and blepharis 'eyelash'), but under the International Code of Zoological Nomenclature (ICZN) the original spelling is retained.[12] The spelling difference affects all higher taxa whose names are derived from this genus: the ICBN recognizes family Katablepharidaceae, order Katablepharidales, class Katablepharidophyceae and phylum Katablepharidophyta, while the ICZN recognizes family Kathablepharididae, order Kathablepharidida, class Kathablepharidea and phylum Kathablepharida.[6]
References edit
Citations edit
- ^ a b c Clay & Kugrens 1999, p. 57.
- ^ Okamoto & Inouye 2005.
- ^ Cavalier-Smith 2004, p. 88.
- ^ Cavalier-Smith, Chao & Lewis 2015, p. 344.
- ^ a b Skuja 1939.
- ^ a b c Okamoto & Inouye 2005, p. 172.
- ^ a b c d e Adl et al. 2019, p. 83.
- ^ Clay & Kugrens 1999, p. 55.
- ^ Nomura, Kamikawa & Ishida 2020.
- ^ a b Vørs 1992, p. 384.
- ^ Clay & Kugrens 1999, p. 43.
- ^ Vørs 1992, p. 370.
- ^ a b Clay & Kugrens 1999, p. 56.
- ^ Cavalier-Smith 1993a.
- ^ Cavalier-Smith 1993b.
- ^ Cavalier-Smith 1997, p. 246.
- ^ Cavalier-Smith 2004, p. 77.
- ^ Okamoto & Inouye 2005, pp. 172–173.
- ^ a b Okamoto & Inouye 2006.
- ^ a b c Okamoto et al. 2009.
- ^ Cavalier-Smith et al., p. 344.
- ^ Guiry 2024, p. 7.
- ^ a b Burki et al. 2012.
- ^ a b Irisarri, Strassert & Burki 2022.
- ^ Reeb et al. 2009.
- ^ Kim & Graham 2008.
- ^ Kim & Archibald 2012.
Cited literature edit
- Adl, Sina M.; Bass, David; Lane, Christopher E.; Lukeš, Julius; Schoch, Conrad L.; Smirnov, Alexey; Agatha, Sabine; Berney, Cedric; Brown, Matthew W.; Burki, Fabien; et al. (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.
- Burki, Fabien; Okamoto, Noriko; Pombert, Jean-François; Keeling, Patrick J. (2012). "The evolutionary history of haptophytes and cryptophytes: phylogenomic evidence for separate origins". Proceedings of the Royal Society of London B: Biological Sciences. 279 (1736): 2246–2254. doi:10.1098/rspb.2011.2301. PMID 22298847.
- Cavalier-Smith, Thomas (1993a). "The Protozoan Phylum Opalozoa". Journal of Eukaryotic Microbiology. 40 (5): 609–615. doi:10.1111/j.1550-7408.1993.tb06117.x.
- Cavalier-Smith, Thomas (1993b). "Kingdom Protozoa and Its 18 Phyla". Microbiological Reviews. 57 (4): 953–994. doi:10.1128/mr.57.4.953-994.1993. PMC 372943. PMID 8302218.
- Cavalier-Smith, Thomas (1997). "Amoeboflagellates and Mitochondrial Cristae in Eukaryote Evolution: Megasystematics of the New Protozoan Subkingdoms Eozoa and Neozoa". Archiv für Protistenkunde. 147 (3–4): 237–258. doi:10.1016/S0003-9365(97)80051-6.
- Cavalier-Smith, Thomas (2004). "Chromalveolate Diversity and Cell Megaevolution: Interplay of Membranes, Genomes and Cytoskeleton". In Hirt, Robert P.; Horner, David S. (eds.). Organelles, Genomes and Eukaryote Phylogeny: An Evolutionary Synthesis in the Age of Genomics. Systematics Association special volume 68. CRC Press. pp. 86–126. ISBN 0-415-29904-7.
- Cavalier-Smith; Chao; Lewis (2015). "Multiple origins of Heliozoa from flagellate ancestors: New cryptist subphylum Corbihelia, superclass Corbistoma, and monophyly of Haptista, Cryptista, Hacrobia and Chromista". Molecular Phylogenetics and Evolution. 93: 331–362. doi:10.1016/j.ympev.2015.07.004. PMID 26234272.
- Clay, Brec; Kugrens, Paul (1999). "Systematics of the Enigmatic Kathablepharids, Including EM Characterization of the Type Species, Kathablepharis phoenikoston, and New Observations on K. remigera comb. nov". Protist. 150 (1): 43–59. doi:10.1016/S1434-4610(99)70008-8. PMID 10724518.
- Guiry, Michael D. (2024). "How many species of algae are there? A reprise. Four kingdoms, 14 phyla, 63 classes and still growing". Journal of Phycology. 60 (2): 214–228. doi:10.1111/jpy.13431.
- Irisarri, Iker; Strassert, Jürgen F. H.; Burki, Fabien (2022). "Phylogenomic insights into the origin of primary plastids". Systematic Biology. 71 (1): 105–120. doi:10.1093/sysbio/syab036. PMID 33988690.
- Kim, Eunsoo; Graham, Linda E. (2008). "EEF2 analysis challenges the monophyly of Archaeplastida and Chromalveolata". PLOS ONE. 3 (7): e2621. Bibcode:2008PLoSO...3.2621K. doi:10.1371/journal.pone.0002621. PMC 2440802. PMID 18612431.
- Kim, Eunsoo; Archibald, John M. (2012). "Ultrastructure and Molecular Phylogeny of the Cryptomonad Goniomonas avonlea sp. nov". Protist. 164 (2): 160–182. doi:10.1016/j.protis.2012.10.002.
- Nomura, Mami; Kamikawa, Ryoma; Ishida, Ken-Ichiro (2020). "Fine Structure Observation of Feeding Behavior, Nephroselmis spp.-derived Chloroplast Enlargement, and Mitotic Processes in the Katablepharid Hatena arenicola". Protist. 171 (2): 125714. doi:10.1016/j.protis.2020.125714.
- Okamoto, Noriko; Inouye, Isao (2005). "The Katablepharids are a Distant Sister Group of the Cryptophyta: A Proposal for Katablepharidophyta Divisio Nova/Kathablepharida Phylum Novum Based on SSU rDNA and Beta-Tubulin Phylogeny". Protist. 156 (2): 163–179. doi:10.1016/j.protis.2004.12.003. PMID 16171184.
- Okamoto, Noriko; Inouye, Isao (2006). "Hatena arenicola gen. et sp. nov., a Katablepharid Undergoing Probable Plastid Acquisition". Protist. 157 (4): 401–419. doi:10.1016/j.protis.2006.05.011. PMID 16891155.
- Okamoto, Noriko; Chantangsi, Chitchai; Horák, Aleš; Leander, Brian S.; Keeling, Patrick J. (2009). "Molecular Phylogeny and Description of the Novel Katablepharid Roombia truncata gen. et sp. nov., and Establishment of the Hacrobia Taxon nov". PLOS ONE. 4 (9): e7080. Bibcode:2009PLoSO...4.7080O. doi:10.1371/journal.pone.0007080. PMC 2741603. PMID 19759916.
- Reeb, Valérie C.; Peglar, Michael T.; Yoon, Hwan Su; Bai, Jennifer Ruoyu; Wu, Min; Shiu, Philip; Grafenberg, Jessie L.; Reyes-Prieto, Adrian; Rümmele, Susanne E.; Gross, Jeferson; Bhattacharya, Debashish (2009). "Interrelationships of chromalveolates within a broadly sampled tree of photosynthetic protists". Molecular Phylogenetics and Evolution. 53 (1): 202–211. doi:10.1016/j.ympev.2009.04.012. PMID 19398025.
- Skuja, Heinrich-Leonhard (1939). "Beitrag zur Algenflora Lettlands II" [Contribution to the algal flora of Latvia II]. Acta Horti Botanici Universitatis Latviensis (in German). 11/12: 41–168.
- Vørs, Naja (1992). "Ultrastructure and autecology of the marine, heterotrophic flagellate Leucocryptos marina (Braarud) Butcher 1967 (Katablepharidaceae/Kathablepharidae), with a discussion of the genera Leucocryptos and Katablepharis/Kathablepharis". European Journal of Protistology. 28 (4): 369–389. doi:10.1016/S0932-4739(11)80001-5. PMID 23195337.