Ultrastructural Studies on a Model Tintinnid - Schmidingerella meunieri (Kofoid and Campbell, 1929) Agatha and Strüder-Kypke, 2012 (Ciliophora). I. Somatic Kinetids with Unique Ultrastructure

Abstract

Molecular phylogenies of Oligotrichea currently do not contain all genera and families and display topologies which are often incongruent with morphological findings. In ciliates, the somatic kinetids are rather conserved, i.e., their ultrastructures, particularly the fibrillar associates, often characterise the main groups, except for the choreotrichids. Four different kinetid types are found in protargol-stained choreotrichids and used for reconstructing the taxon’s evolution (the “Kinetid Transformation Hypothesis”). Proof for this hypothesis requires transmission electron microscopic studies, which are very rare in the choreotrichids and oligotrichids. Such an approach provides insights into the ultrastructural variability of somatic kinetids in spirotrichs and may also detect apomorphies characterising certain choreotrichid families. In the model tintinnid Schmidingerella meunieri, the ultrastructure of the three kinetid types in the somatic ciliature is studied in cryofixed cells. The data support the “Kinetid Transformation Hypothesis” regarding tintinnids with a ventral kinety. This first detailed study on kinetids in tintinnids and choreotrichids in general reveals totally new kinetid types in ciliates: beyond the three common associates, they are characterised by two or three conspicuous microtubular ribbons extending on the kinetids’ left sides. These extraordinary ribbons form together with the overlapping postciliary ribbons a unique network in the cortex of the anterior cell portion. The evolutionary constrains which might have fostered the development of such structures are discussed for the Oligotrichea, the choreotrichids, and tintinnids as their first occurrence is currently uncertain. Additionally, the kinetids in tintinnids, aloricate choreotrichids, oligotrichids, hypotrichs, and euplotids are compared.

Some Ultrastructural Features of the Planktonic Freshwater Ciliate Limnostrombidium viride (Alveolata, Ciliophora, Oligotrichida) and Improved Diagnoses of Oligotrich Taxa

“…In L. viride (this study), Strombidiidae (Agatha and Riedel-Lorjé 1997, Agatha 2004b), and the aloricate choreotrichid Strombidinopsis minima (Agatha 2003b), the dikinetids are anticlockwise inclined to the kinety axis (surface view), while clockwise inclined in euplotids (Ruffolo 1976, Wicklow 1983, Morelli et al 1996) and hypotrichs (Grimes and Adler 1976, Wirnsberger-Aescht et al 1989). The dikinetidal basal bodies extend parallel to each other in euplotids (Ruffolo 1976, Wicklow 1983, Lenzi and Rosati 1993) and hypotrichs (Grimes and Adler 1976), while the posterior ventral and left girdle basal bodies of oligotrichid dikinetids are obliquely orientated (this study, Fauré-Fremiet and Ganier 1970, Modeo et al 2003); data for choreotrichids are not available, but will soon be published for a tintinnid (Gruber et al 2018).…”

“…In tintinnids, the somatic ciliature consists of some dikinetids and many monokinetids, but merely the ultrastructure of monokinetids had been described as yet (Hedin 1976, Laval-Peuto and Brownlee 1986, Laval-Peuto 1994); a detailed investigation on Schmidingerella meunieri will soon be published (Gruber et al 2018). Interestingly, the postciliary ribbons extend parallel to the kinety axis and terminate posteriorly to the second following kinetid, overlapping the postciliary microtubules of the next kinetid; such a pattern is not found in L. viride .…”

Combined Genome and Transcriptome Analyses of the Ciliate Schmidingerella arcuata (Spirotrichea) Reveal Patterns of DNA Elimination, Scrambling, and Inversion

“…2019 ). Although tintinnids have a long history of taxonomic study ( Müller 1779 ; Haeckel 1866 ), there exists no published data on their MIC or genomic architecture, and only limited transcriptome data exist for Schmidingerella ( Keeling et al. 2014 ), the only tintinnid genus with transcriptome data.…”

Morphological, Molecular, and Growth Characteristics of a Cryptic Species, Strombidium parasulcatum n. sp. (Alveolata: Ciliophora: Oligotrichida)

“…Moreover, the ultrastructure and cyst morphology should also be considered (Gruber et al, 2019). However, our study showed that the molecular data could play an important part in the resolution of the cryptic species, as suggested by Santoferrara and McManus (2017).…”

“…To resolve this issue, previous studies suggested that the subtle morphological or ecological differences among the species are required, so we can understand their biogeography and ecological niche differentiation ( McManus et al, 2010 ). Moreover, the ultrastructure and cyst morphology should also be considered ( Gruber et al, 2019 ). However, our study showed that the molecular data could play an important part in the resolution of the cryptic species, as suggested by Santoferrara and McManus (2017) .…”