Protocyclidium citrullus (Cohn, 1866) Foissner, 2002

Omar, Atef & Jung, Ji Hye Choi and Jae-Ho, 2023, New record of ten ciliate species (Protozoa, Ciliophora) from South Korea, Journal of Species Research 12 (1), pp. 95-108 : 104-105

10. Protocyclidium citrullus (Cohn, 1866) Foissner et al., 2002 ( Fig. 10 )

Material examined. Slightly saline fresh water (salinity 0.4‰) collected from Gyeongpo Stream , Unjeong-dong , Gangneung-si, Gangwon-do, Korea (37°47 ʹ 20.02 ʺ N, 128°54 ʹ 34.47 ʺ E) on April 12, 2018 .

Diagnosis. Size 18 - 21 × 9 - 11 μm after protargol impregnation (n = 6); body ellipsoidal, length: width ratio 2: 1; macronucleus in anterior portion of cell, globular with small nucleoli, about 5 μm in diameter, micronucleus inconspicuous; 13 - 15 somatic ciliary rows, each consists of dikinetids in anterior half of body, monokinetids in third quarter, and shortened posteriorly, kinety n-1 with a condensation of 6 or 7 monokinetids posteriorly at level of end of oral apparatus, cilia about 7 μm long, a single caudal cilium about 15 μm long after protargol impregnation; oral apparatus extends to about 2/3 of body length; paroral hook-like, extends anteriorly to beginning of adoral membranelle 1; membranelle 1 consists of few basal bodies, membranelles 2 and 3 hardly distinguishable.

Distribution. Cosmopolitan.

Remarks. The Korean population of Protocyclidium citrullus agrees with the descriptions of Czapik (1963), Wilbert (1995), and Esteban et al. (2000) in most features. The four populations share the body size, the number of somatic kineties. On the other hand, the condensation of basal bodies in the end of kinety n-1 was described in all populations except that of Czapik (1963). However, P. citrullus is unique among congeners in having a condensation of kinetids in posterior end of the significantly shortened kinety n-1 (i.e., terminates posteriorly at the cytostome level). The overall morphology of P. citrullus is also similar to Cyclidium glaucoma but they can be distinguished by the arrangement of membranelles 2 and 3 (indistinguishable vs. separated), the number of somatic ciliary rows (14 - 16 vs. about 10), the length of the somatic kinety n-1 (shortened posteriorly vs. extends to caudal area), and the presence (vs. absence) of the ciliary condensation in somatic kinety n-1 ( Foissner, 1996; Foissner et al., 2002; Song and Wilbert, 2002; Kim et al., 2020).

Voucher slides. One slide with protargol-impregnated specimens was deposited at the National Institute of Biological Resources, Korea (NIBRPR0000110841).

Figures

Fig. 10. Protocyclidium citrullus after protargol impregnation.A, Ventral view showing the oral apparatus and the ventral infraciliature.Arrows denote the condensation of about 6 ciliated kinetids at the end of the shortened kinety n-1. B, Dorsal view showing the dorsal infraciliature. CC, caudal cilium; M1-3, oral membranelles; MA, macronucleus; PM, paroral membrane. Scale bars 10 μm.