Beschreibung:
<jats:p><jats:italic>Frontonia microstoma</jats:italic>, a ciliate living in brackish water, is described. The somatic infraciliature, the buccal in‐fraciliature and the fibrillar buccal system show essential characteristics of species of Frontoniidae Kahl. The number and the arrangement of vestibular kineties are specific. Dark blue‐green pigment is formed by small ectoplasmic vesicles. Formation of cysts is frequent in natural medium and cultures. There is no dedifferentiation of ciliates when encysted. Excystment is induced readily. Thriving cultures of <jats:italic>F. microstoma</jats:italic> have been obtained by feeding the ciliates with appropriate species of Cyanophyceae. Growth was better in brackish water than in either sea water or fresh water.</jats:p>