2. Euplotes rariseta Curds, West and Dorahy, 1974

(Figs. 1 e-h, 4a-f)

Material examined. Korea: Masan Bay (35°10 ʹ 08 ʺ N, 128°35 ʹ 58 ʺ E), 31 May 2016 and Jongdal-ri Beach, Jeju Island (33°30 ʹ 47 ʺ N, 126°53 ʹ 56 ʺ E), 14 July 2018, from marine intertidal sediments, collected by Won Je Lee. Type strains, live cells are kept with the Korean Culture Collection of Protists, Kyungnam University, Korea, reference ‘ KM401 ’ and ‘ KM444 ’.

Description. Cells are 32-44 × 23-35 μm in vivo and 23- 30 × 17-20 μm in protargol, ovoid and dorso-ventrally flattened. The peristome is wide, spindle-shaped and surrounded by 18-22 adoral membranelles, which extend for about 72% of the cell length (Figs. 1e, 1f, 4a, 4 d-f). Cytoplasm colorless. Few food vacuoles and single contractile vacuole located in the middle of the cell (Fig. 4a, 4b). Cirri usually strong; 10 fronto-ventral, 5 transverse, and 2 caudal cirri (Fig. 4b, 4c). Caudal cirrus below AZM is slightly stout. Ventral surface heavily sculptured with 6 longitudinal ridges (Fig. 4b, 4c, arrowheads). Dorsal surface with 6 double-edged longitudinal ridges (Fig. 4a, arrowheads). Dorsal bristles sparse; 6 kinetics (Figs. 1g, 4e). The macronucleus (Ma) is horseshoe-shaped, and the micronucleus (Mi) is small and situated anteriorly (Figs. 1 f-h, 4e). The cells are capable of encystment. Move by crawling on substrate. This species was found at Masan Bay (Korea; Strain KM401) and Jongdal-ri Beach (Jeju, Korea; Strain KM444).

Remarks. Euplotes rariseta was originally reported by Curds et al. (1974) from Aberystwyth, Wales (UK). Our observations are in good agreement with those of Curds et al. (1974), Ma et al. (2007) and Song and Packoff (1997). Euplotes rariseta is similar to E. parabalteatus and E. trisulcatus in cell length, but can be distinguished because E. parabalteatus has 8-11 dikinetids in mid-DK (vs 5-7) and inconspicuous dorsal ridges, and E. trisulcatus has 25-36 AM (vs 18-22) and 7-11 dikinetids in mid-DK, and (Tables 1, 2). This species is mostly similar to E. orientalis in cell length and in the numbers of AM, DK and dikinetids in mid-DK, but they can be distinguished because E. rariseta has 10 FVC (vs 8) and 1 MC (vs 2) (Tables 1, 2). In addition, the 18S rRNA sequences of E. rariseta and E. orientalis have 93% similarity.

NCBI BLASTN search result shows that the closest strains to our strains (KM401, KM444) are E. rariseta stains (GenBank Accession No. AJ305248, FJ423449; Identity 99%). The 18S rRNA sequences of stain KM401 and KM444 are 1,742 bp and 1,738 bp in length, respectively.

Habitat. Marine

Distribution. Korea (Inchon, Park et al., 2017; Masan Bay and Jeju Island, this study), Antarctica (Ross Sea, Valbonesi and Luporini, 1990; Albergoni et al., 2000), Bellings-hausen Sea (Thompson, 1972), China (Song and Packroff, 1997; Jiang et al., 2010b), Indian Ocean (Dallai et al., 1987), Red Sea (Solar lake; Wilbert and Kahan, 1981), Somalia (Gesira; Dallai et al., 1987), UK (Aberystwyth, Wales, Curds et al., 1974), Weddell Sea (Agatha et al., 1990; Petz et al., 1995).

Deposition. National Institute of Biological Resources, Korea (NIBRPR0000107971) for KM401 strain.

NCBI GenBank Accession Numbers: Strain KM 401: MK028833, Strain KM444: MK050525