Material examined. Brackish water with seaweed (salinity, 20‰) collected from Gunsuncheon Stream, Gangdong-myeon, Gangneung-si, Gangwon-do, Korea (37° 44′27″N 128°59′2″E) on 1 May 2019.

Diagnosis. Body size about 150 × 45 μm in vivo, 161- 207 × 40-52 μm after protargol impregnation (n = 6); body contractile, elongated elliptical with slightly bulged oral part; posteriorly located contractile vacuole with 2 distinct collecting canals; cytoplasmic extrusomes scattered throughout body, 6-8 μm in length; cortex punctate by deep ciliary pits; 2 macronuclear nodules; 34-47 monokinetidal somatic kineties with few dikinetids anteriorly; single circumoral kinety; perioral kinety opened and disturbed 3 brush rows.

Distribution. China and Korea.

Remarks. The Korean P. apofuscum population differs from the Chinese population in the presence (vs. absence) of the contractile vacuole’s canals (Long et al., 2009). Paraspathidium apofuscum is different from P. fuscum (Kahl, 1928) Fjeld, 1955 in the number of somatic kineties (34-47 vs. 50-60), the presence (vs. absence) of the dorsal brush, and the opened (vs. closed) perioral kinety (Long et al., 2009).

Voucher slides. Two slides with protargol-impregnated specimens were deposited at National Institute of Biological Resources (NIBRPR0000110199, NIBRPR0000110 200).