Ultrastructure of vegetative cells and resting cysts, and live observations of the encystation and excystation processes in Diophrys oligothrix Borror, 1965 (Protista, Ciliophora)

Abstract

Ciliated protists can form cysts to resist unfavorable environmental conditions and then excyst when environmental conditions become favorable. This study used electron and light microscopy to investigate the structure of vegetative cells and resting cysts, as well as the encysting and excysting processes of Diophrys oligothrix. For the first time, ampules were revealed beneath the pellicle in the genus Diophrys, and their extrusome types differed between Diophrys species. Membrane-packed discs of diverse shapes were found in the cytoplasm just beneath the pellicle around the cytopharynx and were separated by rows of microtubule units. Beneath the discs, some double-layer microtubule structures were detected as well. During encystment, the ventral ciliature was folded in a ventral cavity of the cell, and the caudal cirri were retracted directly into the cyst in a separate cavity on the dorsal side. In the resting cysts, high autophagic activity occurred, possibly including digestion of membrane-packed discs and ampules. Two macronuclear nodules kept their basic shape, although the chromatin aggregation and fusion region were observed in ultrathin sections. The cyst wall contained two layers, namely, the ectocyst, and endocyst. In mature cysts, basal bodies and ciliary shafts were observed, demonstrating that D. oligothrix forms non-kinetosome-resorbing cysts. The process of excystment occurred in two modes, either with or without participation of a contractile vacuole.

An Integrative Investigation of Parabistichella variabilis (Protista, Ciliophora, Hypotrichia) Including Its General Morphology, Ultrastructure, Ontogenesis, and Molecular Phylogeny

“…) and (2) myeloid pharyngeal disks, which are very electron‐dense, have multiple lamellar membranes, and may be rod‐ or ring‐shaped, for example, in Euplotes eurystomus , Certesia quadrinucleata , Diophrys oligothrix , and D. scutum (Fauré‐Fremiet and André ; Gong et al. ; Kloetzel ; Rosati et al. ; Verni and Gualtieri ; Wicklow ).…”

Ultrastructural Features of an Abundant and Ubiquitous Marine Ciliate, Uronychia binucleata (Protista, Ciliophora, Euplotida)

“…However, only a sheet of subpellicular microtubules was described in U. transfuga (Morelli et al, 1996), which could mean that the triad configuration in the dorsal was ignored. These kinds of subpellicular microtubules were rarely reported until now, which have only been observed in some euplotids (Rosati, 1970;Wicklow, 1983;Rosati et al, 1987;Gong et al, 2018) and some cyrtophorids (Hofmann and Bardele, 1987;Kurth and Bardele, 2001), thus, we speculate that the arrangement of the subpellicular microtubules might be one of characteristics of the order Euplotida. The function of these kind of arrangements of subpellicular microtubules is still ambiguous, they may be used for support or remarkable rigidity (Sandborn et al, 1964;Gliddon, 1966), sensory conduction or coordination (Randall and Jackson, 1958;Jerka-Dziadosz et al, 1987;Arregui et al, 1994), and fluid conduction (Sandborn et al, 1964).…”

“…Moreover, this is often considered one of the characteristics of euplotids (Lynn, 2008), as reported in Euplotes (Verni et al, 1978;Dallai and Luporini, 1981;Görtz, 1982;Rosati and Modeo, 2003;Lobban et al, 2005), Diophrys (Rosati, 1970;Gong et al, 2018), Certesia (called muciferous-like bodies; Wicklow, 1983) and Aspidisca (called cytoplasmic vesicles; Rosati et al, 1987). However, the characteristic extrusomes of Uronychia can be easily differentiated from these ampules as follows: (1) they are not observed in vivo vs. being distinctive in vivo; (2) they are arranged in longitudinally oriented rows vs. around the dorsal bristles or ciliary insertion as a "rosette"; (3) most notably, they can be extruded vs. no extrusion process being observed (Fauré-Fremiet and André, 1968;Rosati, 1970;Ruffolo, 1976;Görtz, 1982;Wicklow, 1983;Rosati et al, 1987;Gong et al, 2018). That is to say, in Uronychia, as a notable member of Euplotida, the ampules may not exist.…”

“…The pharyngeal disks in the oral region are the precursors that rapidly form food vacuole membranes (Kloetzel, 1974;Lynn, 2008). They have been classified into two types by Dong et al (2020b): (1) Single-membrane-bound pharyngeal disks with low electron density (for example, in Climacostomum virens, Euplotidium itoi, Parabistichella variabilis and Uronychia transfuga) and (2) myeloid pharyngeal disks with high electron density (for example, in Euplotes eurystomus, Certesia quadrinucleata, Diophrys oligothrix and D. scutum) (Fauré-Fremiet and André, 1968;Kloetzel, 1974;Fischer-Defoy and Hausmann, 1981;Wicklow, 1983;Rosati et al, 1987;Lenzi and Rosati, 1993;Morelli et al, 1996;Verni and Gualtieri, 1997;Gong et al, 2018). The single-membrane-bound pharyngeal disks are present in U. binucleata, interposed with microtubular sheets as reported in U. transfuga (Morelli et al, 1996).…”

Documentation of a new hypotrich species in the family Amphisiellidae, Lamtostyla gui n. sp. (Protista, Ciliophora) using a multidisciplinary approach

“…The cortical granules in Lamtostyla gui are membrane-bounded structures, thus, are potential extrusomes 77 . Considering their morphological characters, i.e., ellipsoidal in shape with bipartite inclusion, they might be assigned to mucocysts, however, considering their distribution, i. e., mainly around bases of cirri and dorsal bristles, they are quiet similar with cortical ampules in the subclass Euplotia Jankowski, 1979 78,79 . Moreover, they are largely packed forehead of the pharyngeal discs in the buccal area, hence, we assume that they might be helpful in food ingestion or pretreatment.…”