Fig 1.
Sampling locations of the three described populations of Euplotes curdsi sp. nov.
The species has been observed in a brackish lagoon in Italy as well as in marine sediments from the Mediterranean and White Sea.
Fig 2.
Morphology of Euplotes curdsi sp. nov., as represented in specimens of the type strain Min1.
(A) Ventral view of a living organism. (B) Nuclear apparatus stained with the Feulgen method. (C) Nuclear apparatus stained by DAPI in a living organism. (D) Superimposed differential interference contrast and fluorescence micrographs of the same specimen. (E) Schematics of argyrome and nuclear features observable on the ventral (left) and dorsal (right) side, drawn from fixed cells (paratypes P1 and P2) with a tracing device. The Wallengreen [48] numerical system for frontoventral cirri numeration is also shown. (F) Ventral view of a living organism, showing the prominent ventral ridges. (G) Ventral argyrome features after silver staining (holotype). (H) Dorsal argyrome features after silver staining (paratype P3). (I) Ventral view of a cell using scanning electron microscopy (SEM). (J) Dorsal view of a cell using SEM. Scale bars represent 10 μm. A small arrow points at the contractile vacuole. Black arrowheads indicate the position of ventral ridges. AZM, adoral zone of membranelles; CC, caudal cirri; Dk, dikinetid; FVC, frontoventral cirri; K, dorsolateral kineties; Mac, macronucleus; MC, marginal cirri; Mic, micronucleus; Pm, paroral membrane; TC, transverse cirri.
Fig 3.
Maximum Likelihood phylogenetic tree of the genus Euplotes based on SSU rRNA gene sequences (46-sequence dataset, 2140 characters).
The outgroup used to root the tree has been omitted. Numbers associated with nodes represent bootstrap/posterior probability; values below 70/0.95 are not shown. Labeled nodes were recovered by all methods and datasets tested (see Materials and Methods). Five major clades are identified by capital letters (A-E). Dashed lines separate 15 smaller subclades. Data on environment, region and ecozone were obtained from published papers or GenBank metadata associated with all available sequences for each species (see also S1 Fig). Unknown information is displayed as empty circles. The arrow points at the representative sequence of Euplotes curdsi sp. nov. The bar represents an inferred evolutionary distance of 5%.
Fig 4.
Evolutionary history of the genus Euplotes.
Phylogenetic relationships are based on recent SSU rRNA gene analyses (see also Fig 3). Colors on branches represent habitats, according to sequence metadata and literature. The 38 morphospecies included were grouped in 15 monophyletic subclades. When species within a subclade did not all share the same environment (see text), majority-rule consensus was applied. Schematic drawings represent the dorsal argyrome type(s) and frontoventral cirral pattern(s) of the species in each subclade (the argyrome type of E. dammamensis is unknown). Dimensions of the drawings correlate with the average size of the species. The character status of ancestors was inferred using a parsimony criterion. Changes in the argyrome type (green) or the number of frontoventral cirri (red) are shown on branches. Intra-subclade variability is highlighted with colored boxes: red-shaded cirri were lost and green-shaded dargyrome types were acquired by the marked species. The establishment of the obligate symbiosis between Euplotes species and the betaproteobacterium Polynucleobacter is also shown.
Table 1.
Morphological comparisons between Euplotes curdsi sp. nov. and five similar species.
Characters that are unambiguously different are in bold.