The stomatogenesis and morphology of the marine planktonic ciliate Philasterides armatalis collected from mollusc-culturing waters off the coast of Qingdao, China, were studied using a differential interference contrast microscope for observations in vivo and protargol impregnation. In terms of its infraciliature, this species possesses typical characteristics of the genus Philasterides: bipartite paroral membrane, the anterior part double-rowed and the posterior part in a zig-zag-formation, and three well-defined membranelles arranged in Paranophrys-pattern. This investigation confirms the dual origin of the buccal apparatus in the opisthe, one derived from the scutica and the other from the paroral membrane. Its stomatogenesis belongs to the ‘Philasterides’ sub-type, although it differs from its only congener P. armata, in that paroral membrane 1 gives rise to the paroral membrane and the scutica in the proter, and paroral membrane 2 forms the paroral membrane, membranelles 1 and 2 and the scutica in the opisthe. Based on stomatogenetic data, the phylogenetic positions of several genera in the suborder Philasterina are reconsidered.