title: Life cycle dependent phototactic orientation in Ophryoglena catenula.
abstract: The histophagous ciliate Ophryoglena catenula, which is characterized by a conspicuous "watchglass organelle", shows a pronounced orientation with respect to the direction of light. The five stages of the common reproduction cycle are all light sensitive: Positive phototaxis was regularly found in "theronts" exposed to unilateral white light at intermediate fluence rates (e.g. 10 klx), and also in "trophonts" and "protomonts" within 2.5 hours after feeding. Negative phototaxis was observed under identical experimental conditions in "protomonts" about 5 h after feeding as well as in "tomonts" and "tomites" which had settled down and were mechanically irritated. In contrast to these stages individuals of a rarely occurring "migratory stage" are insensitive to light. Theronts which were exposed to an attractive chemical stimulus immediately interrupted their oriented movement towards the direction of the light, showing near random orientation or following the chemical gradient. Phototaxis in Ophryoglena is discussed in terms of its significance for orientation in the natural environment of these ciliates.
authors.affiliation: Institut für Allgemeine Zoologie und Genetik der Universität Münster, Münster, Germany.
authors.forename: H W
authors.initials: HW
authors.lastname: Kuhlmann