Euplotes encysticus Yonezawa, 1985

Kim, Eun-Hee & Lee, Won Je, 2019, Redescriptions of Euplotes encysticus and E. rariseta (Protist: Ciliophora: Euplotida), Journal of Species Research 8 (1), pp. 128-135 : 130-132

1. Euplotes encysticus Yonezawa, 1985 ( Figs. 1 a-d, 2, 3)

Material examined. Korea: Dokdo (37°14 ʹ 22 ʺ N, 131° 52 ʹ 08 ʺ E), 27 September 2017, from a freshwater pond (Mulgol), collected by Jong Soo Park. Type strain, live cells are kept with the Korean Culture Collection of Protists , Kyungnam University , Korea, reference ‘KF403’.

Description. Cells are 63-79 × 41-61 μm in vivo and 44-56 × 28-38 μm in protargol, asymmetrically oval with posterior portion slightly wider than anterior, and dorso-ventrally flattened. The peristome is narrow and extremely long, extending approximately 72% of cell length and surrounded by 31-36 adoral membranelles. Adoral zone of membranelles (AZM) curved ( Figs. 1a, 1b , 2a, 2d, 2f ). Cytoplasm colourless, often filled with many light reflecting granules and few food vacuoles ( Fig. 2a ). Single contractile vacuole located to right of transverse cirri (TC) ( Fig. 2a ). Seven dorso-lateral ridges ( Figs. 2b , arrowheads; 2e). Dorsal kineties (DK) inserted in concaves down the ridges ( Figs. 1c , 2e ). The kinetosome number of the mid-dorsal kinety is 19- 22. Cirri usually strong; 9 fronto-ventral, 5 transverse, 2-3 (mostly 2) caudal and 2 left marginal cirri. Paroral membrane (PM) about 10 μm long. Macronucleus (Ma) usually C-shaped, with the anterior and posterior ends sometimes curving ( Figs. 1d , 2d, 2f ). Micronucleus (Mi) small, nearly spherical and located in the upper right half of the macronucleus ( Figs. 1b, 1d , 2d ). The cells are capable of encystment and excystment ( Fig. 3 ). Move by crawling on crumb or substrate.

Remarks. Euplotes encysticus was originally reported by Yonezawa (1985) as a freshwater form. We performed the inoculation of our strain KF403 into well plates containing seawater (15 and 30 psu) with barley grains. The strain grew well in the seawater, thus this species is adaptable to both seawater and freshwater. Our observations are in accord with those of Yonezawa (1985) and Fan et al. (2010). Euplotes encysticus is very similar to E. muscorum in general appearance, but according to several researchers (e.g., Dragesco, 1970; Dragesco and Dragesco Kernéis, 1986; Jo and Shin, 2003) they can be distinguished from each other because (1) no cyst has been observed so far in E. muscorum , (2) the obvious dorsal-lateral ridges and the granules surrounding the dorsal cirri have not observed in E. muscorum , (3) the AZM of E. encysticus outspreads more broadly than that of E. muscorum , and (4) the AZM covers 3/4 body length in E. encysticus , and 2/ 3 in E. muscorum . Our strain has all of these characters specific to E. encysticus . Additionally, these two species are clearly distinguished by the differences in their 18S rRNA gene sequences, of which E. encysticus differs from E. muscorum by 2.04% ( Fan et al., 2010). Euplotes encysticus is similar to E. petzi , E. roscoffensis and E. sinicus in cell length, but the numbers of AM, DK and dikinetids in mid-DK in E. encysticus are higher than those in E. petzi . Euplotes roscoffensis and E. sinicus have higher number of AM than that of E. encysticus ( Tables 1 , 2 ). Euplotes sinicus has 11-16 dikinetids in mid-DK (vs 5-7) ( Tables 1 , 2 ).

NCBI BLASTN search result shows that the closest strains to our strain KF403 are E. encysticus stains [GenBank Accession Nos. FJ346569 , EF535728 , LN864512 ; Identity 99%]. The 18S rRNA sequence of our stain is 1,663 bp in length.

Habitat. Marine and Freshwater

Distribution. Freshwater habitats: Korea (Dokdo, this study), Japan ( Yonezawa, 1985) Marine habitats: China (Daya Bay, Fan et al., 2010)

Deposition. National Institute of Biological Resources, Korea (NIBRPR0000109440)

NCBI GenBank Accession Number: MK026950

Figures

Fig. 1. Drawings of Euplotes encysticus (a-d) and E. rariseta (e-h). (a) E. encysticus and (e) E. rariseta in vivo, E. encysticus (b-d) and E. rariseta (f-h) after protargol impregnation. (b) and (f) ventral views, (c) and (g) dorsal views, (d) and (h) different shapes of macronucleus. AZM, adoral zone of membranelles; PM, paroral membrane; FVC, fronto-ventral cirri; TC, transverse cirri; CC, caudal cirri; MC, marginal cirrus; DK, dorsal kineties; Ma, macronucleus; Mi, micronucleus.Scale bars in (b) for (a-c) and in (d) represents 20μm, in (f) for (e-g) and in (h) represent 10 μm.

Fig. 2. Micrographs of Euplotes encysticus strain KF403 (a-c) in vivo and (d-f) after protargol impregnation. (a) Dorsal views showing contractile vacuole (CV) and adoral membranelles, (b) dorsal ridges (arrowheads), (c) ventral side showing FVC (fronto-ventral cirri) and TC (transvers cirri), (d) ventral view showing AZM (adoral zone of membranelles), PM (paroral membrane), FVC, TC, CC (caudal cirri), MC (marginal cirri), Ma (macronucleus), Mi (micronucleus), (e) dorsal side showing DK (dorsal kineties), (f) note 3 CC. Scale bars in (c) for (a-c) and in (f) for (d-f) represent 20 μm.

Fig. 3. Micrographs of excystment of Euplotes encysticus. (a) Cyst of cell 1, (b-j) time series lasting 6 minutes 52 seconds documenting excystment of cell 2, (i) empty cyst and trophozoit, (j) trophozoit.All images are DIC images. Scale bar in(j)=25μm.