Abstract: The marine oligotrichous ciliate Spirotontonia taiwanica n. sp. isolated from the coastal waters of northeastern Taiwan is reported, using live observation, protargol preparations and molecular data. The new species differs from the most similar, known congener Spirotontonia turbinata in the following features: (1) lower number of buccal membranelles (11-13 vs. 13-17); (2) higher number of whorls of girdle kinety (2.5 vs. 1.5); (3) lower number of macronuclear nodules (20-31 vs. 28-40); (4) larger cell size (80-104 x 40-72 vs. 44-75 x 29-56 microm); (5) larger anterior cell end to buccal vertex (50 vs. 33 microm); (6) larger ratio of cell length to cell width (1.74 vs. 1.38); (7) the different beginning of the girdle kinety (posterior to the buccal vertex vs. left of the buccal zone portion); and (8) the disappearance of the L-shaped argyrophilic structures in the last half whorl and occasionally the first 1-10 dikinetids (i.e. yes vs. no). The molecular data also reveal two distinct species, deviating by 2% or 33% base pairs.