Fig 1.
Morphology of Raphidocystis tubifera.
(A in DIC; B–D in PhC; E, F, K, I, M – SEM; G, H, J, L – TEM). A, B – living cells; C – plate scales; D – progenitor cell of the HF-68Z strain; E – general view of the dried cell; F – trumpet-shaped scale Sc.1; G – distal part of scale Sc.1; H – proximal part of scale Sc.1; I, J – funnel-shaped scales Sc.2; K – proximal part of scale Sc.2; L, M – plate-scales. Abbreviations: a – axopodia; sp.sc1 – scale Sc.1; sp.sc2 – scale Sc.2; pl.sc – plate scale; mtoc – microtubule organizing center. Scale bars: A, B, D, E – 10 µm; C – 2 µm; F, I, J, L, M – 1 µm; G, H, K – 0.5 µm.
Fig 2.
Morphology of Raphidocystis tubifera.
(A–C, G, H – SEM; D–E, I – TEM) A, B – Abnormally formed Sc.1; C, D – transitional type of scale from plate-scales to Sc.2; E – underdeveloped teratological plate-scale; F–I – teratological plate-scales with extra axes. Scale bars: 1 μm.
Fig 3.
Morphology of Raphidocystis tubifera.
(A, C, D in PhC; B in DIC; D, E – TEM (inverted); F – SEM) A – cyst in early development; B – mature cysts; C–E, G – empty envelopes of dead cysts consisting of plate-scales; F – a part of the cyst envelope with small plate-scales. Scale bars: A–D, G – 10 μm; E – 5 μm; F – 1 μm.
Fig 4.
Morphology of Raphidocystis ambigua (A in DIC; B– SEM; C–E – TEM)
A – general view of the living cell; B – general view of the dried cell; C – plate-scale of the first type; D – plate-scale of the second type; E – plate-scales of the third type. Scale bars: A, B – 10 μm; C–E – 2 μm.
Fig 5.
Morphology of Raphidocystis marginata.
(A in DIC; B, C – SEM; D–F – TEM) A – general view of the living cell; B – general view of the dried cell; C–F – plate-scales. Scale bars: A, B – 10 μm; C – 2 μm; D–F – 1 μm.
Fig 6.
Morphology of Raphidocystis symmetrica.
(A and F in DIC; B, C – TEM; D–E – SEM) A – general view of the living cell; B – general view of the dried cell; C, D– plate-scales; E, F – cysts. Scale bars: A, B, E, F – 10 μm; C, D – 1 μm.
Fig 7.
Bayesian phylogenetic tree generated from 18S rRNA gene sequences of 42 centrohelids (seven of which represent the outgroup).
Bayesian posterior probabilities (BPP) and Maximum Likelihood (ML) bootstrap values are indicated at branches (BPP > 0.50 and ML bootstrap > 50% are shown; dt – different topology). Filled circles of different colours indicate values of BPP = 1.00 and ML bootstrap = 100%. The sequences generated in this study are highlighted in bold, colored in red and marked with black stars symbols. The percentage of similarity of the sequences is indicated to the right of the names of the sequences. Abbreviations: B, brackish environment: F, freshwater environment; M, marine environment; S, soil environment.
Fig 8.
Feeding of raphidocystid heliozoans by cyanobacteria.
(A1, B1, C1, A3, B3, C3 in DIC; A2, B2, C2, A4, B4, C4 in bright field). A1–A4 – R. tubifera HF-68Z with ingested cells of M. aeruginosa; B1–B4 – R. marginata HF-64Z with ingested cells of M. aeruginosa; C1– C4 – R. symmetrica HF-80Z with ingested cells of M. aeruginosa. Red arrows show ingested cyanobacterial cells. Scale bars: 10 μm.
Fig 9.
Comparison of the morphometric parameters of Raphidocystis contractilis strain Nies-2498 (Wan et al. 2023) and R. marginata strain HF-64Z.
Fig 10.
General view of living cells of Raphidocystis symmetrica.
A – R. symmetrica HF-80Z strain (PhC), the inset shows plate-scales (DIC); B – drawing of R. symmetrica (182 p., as Raphidiophrys symmetrica) by Penard [27]; C – drawing of R. symmetrica (77 p., Plaat 19, as Raphidiophrys symmetrica) by Siemensma [61]. Scale bar: A –10 μm, inset – 5 μm.