Abstract: Diophrys species are a group of marine cosmopolitan free-living ciliates,therefore there are many reports concerning their morphology and diversity.However,species identification remains problematic owing to the fact that many previous descriptions were basically based on live observation and morphometric,and infraciliature data still re-main lacking for some known species.The aims of this paper were to supply new information and to clarify confusions of two known Diophrys species,D.scutum(Dujardin,1841) Kahl,1932 and D.apoligothrix Song et al,2009.Both organisms were collected from the upper layer of sandy sediments in the intertidal region in Qingdao,China,where the water temperature was about 18℃ and the salinity was 18‰.After isolation,pure cultures were kept,to which some rice grains were added to enrich bacterial food.Ciliates were examined in vivo using bright field and differential interference contrast microscopy.The infraciliature was revealed with protargol staining method.Counts and measurements of stained specimens were performed at a magnification of 1250 ×.Based on present and previous studies,an improved diagnosis was presented here for D.scutum: marine Diophrys,broadly oval body outline,in vivo 80-200 μm long;43-80 adoral membranelles and the distal end of adoral zone was strongly curved;5-8 frontoventral,5-6 transverse,2-3 left marginal and 3-4 caudal cirri;5-9 dorsal kineties,which were always densely ciliated;usually two(rarely one) sausage-shaped macronuclear nodules.D.apoligothrix was a rare species,and the current population of it was morphologically identified by:(35-75) μm ×(25-40) μm in vivo;body rigid with sculptured surface;adoral zone comprising about 24-31 membranelles;5 frontal,2 ventral,5 transverse,1 left marginal and 3 caudal cirri;5 dorsal kineties and the middle kinety had about 5-6 basal body pairs,dorsal cilia about 5-10 μm;usually two ellipsoid macronuclear nodules;marine habitat.By now,nine morphospecies were included in the genus Diophrys,namely D.scutum,D.appendiculata,D.oligothrix,D.peloetes,D.kahli,D.salina,D.multinucleata,D.japonica and D.apoli-gothrix.Among these forms,D.oligothrix and D.peloets were very similar to D.scutum.However,D.oligothrix dif-fered from D.scutum in:(1) slender body shape(vs.broadly oval body shape);(2) lower number of adoral membra-nelles(25-37 vs.50-80);(3) the distal end of adoral zone was slightly curved(vs.strongly curved).According to former research,D.peloetes was separated from D.scutum by having 8 dorsal kineties and fewer cilia per kinety.How-ever,based on data available and morphometric comparison,D.peloetes might be regarded as a junior synonym of D.scutum.Compared with other Diophrys species,D.japonica was closely related to D.apoligothrix.But the former could be distinguished from the later in having fewer dorsal kineties(4 vs.5),more basal body pairs per kinety(10 vs.5-6),higher number of adoral zone membranelles(30-46 vs.24-31),cortical granules and 2-5 basal body pairs located close to the proximal membranelles.