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Draft:Psilotrichides

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  • Comment: When the citations are all piled in a heap at the bottom, it isn't clear which source supports what content here. For example, ref #5 doesn't seem to mention Psilotrichides, and it's therefore difficult to see how it could verify anything in this draft – perhaps it does, but I've no idea what?
    Also, please cite online sources for ease of verification; I believe all five are available online. See WP:REFB for advice on referencing. DoubleGrazing (talk) 10:58, 11 December 2025 (UTC)

Psilotrichides is a genus of middle-sized ciliate protists belonging to the family Psilotrichidae, within the Subclass Hypotrichia.[1][2] The genus was established by Heber, Stoeck, and Foissner in 2014 (with a correction published in 2018) as part of a taxonomic revision of the Psilotrichidae family.[1]

The genus is defined by a unique combination of morphological features, including a strongly and distinctly obliquely oriented buccal cavity and a distinct ridge along the right buccal margin.[1][3] The systematic classification of Psilotrichides remains ambiguous in single-gene phylogenetic trees, making it a critical subject for ongoing phylogenomic studies of ciliate evolution.[1][3]

Psilotrichides hawaiiensis is a species of middle-sized ciliate protist belonging to the Subclass Hypotrichia.[1] It is the sole accepted species and type species of the genus Psilotrichides, which was formally established by Heber, Stoeck, and Foissner in 2014.[1] The species is endemic to ephemeral freshwater habitats[1] and is recognized for its highly distinctive cell morphology and its status as a mixotroph.[1][3]

The organism is readily identifiable by its peculiar body shape, which is often described as resembling a "table tennis racket".[1] This shape is a result of a prominent, elongated cirrus located at the terminus of the left marginal row.[1] Its systematic position is highly relevant in eukaryotic studies due to the unusual development of its oral structures and its unresolved phylogeny.[1][3]

Taxobox (classification table)

Rank Taxon Notes Authority
Domain Eukaryota Complex cells with a nucleus.
Phylum Ciliophora The group of protists characterized by cilia. [2]
Class Intramacronucleata A class of ciliates including hypotrichs. [2]
Subclass Hypotrichia Ciliates with a flattened body and specialized bundles of cilia called cirri on the ventral (underside) surface for crawling. [2]
Order Stichotrichida Ciliates defined by having their fused cilia (cirri) primarily arranged into rows running along the ventral surface or edges of the cell. [2]
Family Psilotrichidae The family that defines the core characteristics of Psilotrichides Bütschli, 1889[2]
Genus Psilotrichides The specific group, currently known to be monotypic (containing only one accepted species). Heber, Stoeck & Foissner, 2014[1]
Species P. hawaiiensis The sole accepted species and morphological exemplar, recognized by its "table tennis racket" shape and mixotrophic lifestyle. Heber, Stoeck & Foissner, 2014[1]

Classification and phylogeny

Psilotrichides hawaiiensis is classified within the Family Psilotrichidae, alongside the genera Psilotricha, Urospinula, and Hemiholosticha.[3][2] The family is currently placed within the Subclass Hypotrichia, a diverse group of ciliates characterized by complex cirral patterns.[2]

Molecular studies utilizing the 18S ribosomal RNA (SSU rDNA) gene support the Psilotrichidae as a highly supported monophyletic clade.[1][3] However, the SSU rDNA marker provides insufficient resolution to precisely define the deeper evolutionary relationships of Psilotrichidae within the larger oxytrichid clade of the Hypotrichia.[1][3] This lack of molecular signal, despite the group's extreme morphological novelty, suggests the lineage may be an ancient or rapidly evolving branch within the ciliate tree.[1]

The systematic position of the genus remains dynamic. Based on refined morphological and molecular data, recent analyses have proposed the establishment of a new family, Hemiholostichidae nov. fam., specifically to accommodate Psilotrichides, Hemiholosticha, and Urospinula.[4]

Morphology and ontogenesis

Psilotrichides hawaiiensis in vivo (a, d-g) and after protargol impregnation (b, c). a ventral view of a representative individual. b, c Ventral (b) and dorsal (c) views of a representative specimen, showing ciliature and nuclear apparatus, arrows show the postoral cirri, hatched lines show cirri originating from the same cirral anlage. d-g Ventral views of representative individuals, arrowheads show the red eyespots of the green algae, arrow in (e) indicates the buccal ridge, arrows in (f) indicate the dorsal bristles, arrow in (g) shows the micronucleus. AZM, adoral zone of membranelles; CV, contractile vacuole; EM, endoral membrane; FV, food vacuole; LM, left marginal row; Ma, macronuclear nodules; Mi, micronucleus; PM, paroral membrane; RM, right marginal row; R1-4, ventral rows; TC, terminal cirrus; 1-3, dorsal kineties. Scale bars: 25 μm
Hemiholosticha kahli nov. spec. in the scanning electron microscope. a-d Ventral views of representative individuals, showing cirral pattern, arrows indicate postoral cirri, arrowheads show the long posterior dorsal bristles, hatched lines show cirri originating from the same cirral anlage. e, f Details of anterior end of cells, showing structure of paroral membrane and adoral membranelles. g, h Dorsal views of representative individuals, showing the sharp ribs and dorsal kineties, arrowheads indicate the long posterior dorsal bristles. i Lateral view, showing the convex dorsal side and sharp ribs on dorsal side. j View from posterior body end, showing the sharp ribs on dorsal side. AZM, adoral zone of membranelles; LM, left marginal row; M1-4, ciliary rows of adoral membranelles; PM, paroral membrane; RM, right marginal row; R1-3, ventral rows; 1-3, dorsal kineties. Scale bars: 15 μm

P. hawaiiensis is a middle-sized ciliate, measuring approximately 65 µm in length and 45 µm in width, typically exhibiting significant dorsoventral flattening.[1] It possesses two macronuclear nodules and a single micronucleus.[1]

The diagnostic morphological features that necessitated the creation of the Psilotrichides genus are primarily located in the oral region :[1]

  • Body Shape: The most recognizable trait is the blunt, pyriform (pear-shaped) body plan with a "table tennis racket" outline, caused by a prominent, elongated cirrus that serves as the final cirrus of the left marginal row.[1]
  • Buccal Apparatus: The species possesses a strongly and distinctly obliquely oriented buccal cavity. A key structural marker is the presence of a distinct ridge that runs along the right buccal margin.[1]

A major shared characteristic of the entire Psilotrichidae family is a unique developmental process during asexual division (ontogenesis): the formation of the oral primordium occurs in a deep, internal pouch.[1][3] This derived morphogenetic pattern is considered a significant systematic marker for the family, emphasizing its isolated evolutionary trajectory.[1]

Ecology and distribution

The type population of P. hawaiiensis was originally collected from an ephemeral swamp on Oahu Island, Hawaii.[1] The species has also been recorded from Japanese rice fields.[1]

Subsequent studies have confirmed that Psilotrichides has a broader geographical distribution, with populations documented in China and on the island of Guam.[3] The co-discovery of P. hawaiiensis and a closely related, algae-bearing species (Hemiholosticha kahli) in the same puddle on Guam suggests the ciliate family may be globally undersampled and highly diverse.[3]

Mixotrophy

P. hawaiiensis is a mixotrophic organism.[1][3] Its characteristic green coloration is caused by the presence of intracellular green algae, which it hosts as endosymbionts.[1][3] This dual nutrition strategy combining heterotrophy (preying on other microbes) with phototrophy (using the energy from its algal partners) is thought to be an adaptation that allows the ciliate to thrive in fluctuating environments like ephemeral wetlands where resources may be scarce or unpredictable.[1][3] The specific identity of the intracellular algal species is currently unknown and requires further molecular investigation.[3]

Scientific significance

The research into Psilotrichides hawaiiensis is significant for addressing major systematic challenges within microbial eukaryotes:[1][3]

  • Phylogenomic Necessity: The ambiguous branching position determined by the single SSU rDNA marker highlights P. hawaiiensis as a crucial target for high-resolution, multi-gene sequencing efforts.[1][3] Phylogenetic inferences derived from transcriptomic and/or genomic data are necessary to definitively resolve the systematic position of the Psilotrichidae family within the Hypotrichia subclass.[3]
  • Ontogenetic Evolution: The unique development of its oral primordium in a deep pouch provides vital comparative data for reconstructing the evolutionary trajectory of complex cell division patterns (morphogenesis) across the Ciliophora phylum.[1]
  • Model for Symbiosis: Its obligate or facultative association with intracellular green algae makes it an important model for studying the cytological mechanisms and ecological dynamics of protist-algal endosymbiosis.[3]

References

  1. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae Heber, D; Stoeck, T; Foissner, W (May–June 2014). "Morphology and ontogenesis of Psilotrichides hawaiiensis nov. gen., nov. spec. and molecular phylogeny of the Psilotrichidae (Ciliophora, Hypotrichia)". J Eukaryot Microbiol. 61 (3): 260–77. doi:10.1111/jeu.12104. PMC 4258088. PMID 24498929. Erratum in: J Eukaryot Microbiol. 2018 Mar;65(2):291-292. doi: 10.1111/jeu.12487.{{cite journal}}: CS1 maint: postscript (link)
  2. ^ a b c d e f g h Lynn, D H (2008). yes (ed.). The ciliated protozoa: characterization, classification, and guide to the literature (3 ed.). Springer. ISBN 978-1-4020-8239-9.
  3. ^ a b c d e f g h i j k l m n o p q r Luo, X; Huang, JA; Li, L; Song, W; Bourland, WA (June 18, 2019). "Phylogeny of the ciliate family Psilotrichidae (Protista, Ciliophora), a curious and poorly-known taxon, with notes on two algae-bearing psilotrichids from Guam, USA". BMC Evol Biol. 19 (1): 125. Bibcode:2019BMCEE..19..125L. doi:10.1186/s12862-019-1450-z. PMC 6582579. PMID 31215407.
  4. ^ Vďačný, P; Foissner, W (2021). "Morphology and ontogenesis of two new Hemiholosticha species (Ciliophora, Hypotrichia, Hemiholostichidae nov. fam.)". European Journal of Protistology. 77 125763. doi:10.1016/j.ejop.2020.125763. PMID 33307357.
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