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.[13]
Description
Morphology
Katablepharids are flagellates, unicellularprotists 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][11]
Nutrition
These flagellates feed by ingesting other eukaryotes through a cytostome supported by bands of longitudinal microtubules.[11] One species, Kathablepharis hyalurus, has secondarily lost the cytostome.[14] 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.[15]
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.[16] However, she did not assign this family to any higher taxon, and instead treated it as incertae sedis protists, thereby removing them from Cryptophyceae.[19]
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.[20][21] 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.[22] Because this scheme was based on the observations on a single species K. ovalis, it was not considered valid.[19]
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.[23] 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.[24][a] In the following years, two new genera of katablepharids were described: Hatena in 2006[25] and Roombia in 2009.[9]
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.[4] 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.[11][26]
Classification
There are five accepted genera of katablepharids:[11]
^ abcAccording 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.[18] 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]
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 (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.
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. PMID10724518.
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. hdl:10261/260944. PMID33988690.
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.
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. PMID23195337.