Abstract: The morphology and morphogenesis of Sterkiella histriomuscorum, which was collected from the upper layer of sandy sediments in the intertidal region Qingdao, China, were investigated by examination of in vivo and silver impregnation specimens. As a brackish form, our population matched almost perfectly with former terrestrial and freshwater ones in living morphology and infraciliature: long elliptical outline, size (100-160) mm (40-75) m; no cortical granules were observed; 29-38 adoral membranelles; three frontal, four frontoventral, three postoral ventral, two pretransverse ventral, and 3-5 transverse cirri; left and right marginal rows were composed of 17-23 and 20-24 cirri, respectively; six dorsal kineties; two macronuclear nodules. Its morphogenetic characters were summarized as follows: (1) the old adoral zone of membranelles were retained in situ by the proter, the old undulating membranes were reorganized, and the opisthes oral primordium formed de novo; (2) five frontoventral-transverse anlagen were formed in the secondary-mode and generated the new cirri in a 2:3:3:4:4 pattern; (3) the anlagen of marginal row and dorsal kineties were formed intrakinetally within the parental structure; (4) the formation of dorsal ciliature was in the typical Oxytricha-pattern; (5) the macronuclear nodules fused into a single mass during division.