Euplotes focardii Valbonesi and Luporini, 1990

Yeo, Jeong Hyeon & Jung, Pablo Quintela-Alonso and Jae-Ho, 2023, New record of five Euplotes species (Protozoa, Ciliophora) collected from South Korea, Journal of Species Research 12 (3), pp. 203-211 : 204-205

1. Euplotes focardii Valbonesi and Luporini, 1990

( Fig. 1 )

Material examined. Marine water (salinity 34.9‰, temperature 21℃) collected from Seobudu , Geonib-dong, Jeju-si, Jeju-do, Korea (33°31′2″N, 126°32′3″E) on February 20, 2020 .

Diagnosis. Body size 53.9-72.7 × 41.7-58.8 μm (on average 65.1 × 47.1 μm) after protargol impregnation, shape ellipsoidal, 6 dorsal and 3 ventral ridges (shorter ventral ridges between frontoventral cirri are not included); macronucleus C-shaped, with a single small spherical micronucleus attached to it; 49-56 adoral membranelles; 10 frontoventral, 5 transverse, 2 caudal and 2 marginal cirri; 9 or 10 dorsal kineties, of which the middle kinety composed of about 15-20 dikinetids; dorsal argyrome pattern of double- eurystomus type.

Distribution. Antarctica ( Valbonesi and Luporini, 1990b) and Korea (present study).

Remarks. The Korean population resembles the type population except for the dorsal (distinct vs. indistinct) and ventral ridges (3 vs. 2) ( Valbonesi and Luporini, 1990b). These populations were collected from marine environments and the other morphometric data correspond each other. The identification of E. focardii is rather complex due to the strong overlapping of morphometric data among several Euplotes species (e.g., body size, adoral membranelles, cirri, dorsal kineties). Euplotes focardii morphologically resembles E. neapolitanus Wichterman, 1964 , E. platystoma Dragesco and Dragesco-Kernéis, 1986 and E. shanghaiensis Song et al., 1998 . Euplotes neapolitanus differs from E. focardii by the body size (130-150 × 70-75 μm vs. 38-110 × 30-92 μm), the shape of anterior body end (truncated vs. rounded) and the arrangement of marginal and caudal cirri (evenly distributed vs. a distinct gap between marginal and caudal cirri) ( Curds, 1975; Liu et al., 2020). Euplotes shanghaiensis can be distinguished from E. focardii by the body shape (D-shaped vs. ellipsoidal), the number of dorsal kineties (12 or 13 vs. 9 or 10) and the habitat (freshwater vs. marine) ( Song et al., 1998).

Based on the original descriptions, E. platystoma differs from E. focardii in the number of dorsal kineties (11 vs. 10), the arrangement of marginal and caudal cirri (evenly distributed vs. a distinct gap between marginal and caudal cirri), and the habitat (brackish water vs. marine) ( Dragesco and Dragesco-Kernéis, 1986; Valbonesi and Luporini, 1990b). However, recent descriptions blur the boundary between these two species. For instance, the number of dorsal kineties varies among E. platystoma populations (11 in the type and Shenzhen populations, 13 in Shanghai population, and 10 or 11 in Huizhou population). Regarding the habitat, the type population was collected from brackish water, while Lian et al. (2018) sampled two populations from freshwater and brackish water (6‰), respectively. In addition, while Dragesco and Dragesco-Kernéis (1986) did not include any information about the dorsal ridges in the type population, Lian et al. (2018) and Yan et al. (2018) described the ridges as indistinct or absent, respectively. Interestingly, according to Lian et al. (2018), the small subunit ribosomal RNA gene sequences of the Shanghai population (13 dorsal kineties, brackish water) and Shenzhen population (11 dorsal kineties, freshwater) are identical. Considering the gap between marginal and caudal cirri, it varies among populations (evenly distributed in the Huizhou population vs. a distinct gap in Shanghai and Shenzhen populations) ( Lian et al., 2018; Yan et al., 2018). In conclusion, when considering the features analyzed in both the original and recent redescriptions of E. platystoma and E. focardii , the main differences between these two species lie in their habitat preferences (fresh to brackish water vs. marine) and genetic markers (as depicted in the tree by Liu et al., 2020, they are clearly distinct from each other).

Voucher slides. One slide with protargol-impregnated specimens (NNIBRPR25655) and one slide with wet silver nitrate-impregnated specimens (NNIBRPR25656) were deposited at the Nakdonggang National Institute of Biological Resources, Sangju, Republic of Korea.

Figures

Fig. 1. Euplotes focardii in vivo (A) and after protargol (B, C) and “wet” silver nitrate impregnation(D). A-D. Ventral (A, C) and dorsal (B, D) views of two specimens showing the infraciliature and the three ventral and six dorsal ridges. E. Dorsal argyrome in double-eurystomus pattern.AZM, adoral zone of membranelles; CC; caudal cirri; DK, dorsal kineties; FVC, frontoventral cirri; MC, marginal cirri. Scale bars: 20μm.