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Eyes and vision in Arion rufus and Deroceras agreste (Mollusca; Gastropoda; Pulmonata): What role does photoreception play in the orientation of these terrestrial slugs?
Authors:Marina V. Zieger  Irina A. Vakoliuk  Oksana P. Tuchina  Valery V. Zhukov  Victor Benno Meyer‐Rochow
Affiliation:1. School of Engineering and Science, International University of Bremen (Jacobs University as of February 2007), Research II, Campus Ring 6, D‐28759 Bremen, Germany;2. Department of General and Ecological Physiology of Human and Animals, Faculty of Bioecology, Immanuel Kant University of Russia, Universitetskaya ulitsa 2, 236040 Kaliningrad, Russia;3. Department of Agricultural and Soil Ecology, Faculty of Bioresources and Natural Usage, Kaliningrad State Technical University, Sovetsky avenue, 1, 236000 Kaliningrad, Russia;4. Department of Biology, Faculty of Sciences, University of Oulu, SF‐90014, PO Box 3000, Oulu, Finland
Abstract:This paper deals with the orientational behaviour in the two terrestrial slugs Arion rufus and Deroceras agreste. It presents anatomical details of their eyes and provides an appraisal of the eyes’ optical system. In both species the retinae contain two principal types of cell: photoreceptive and pigmented supportive cells. While only the eye of A. rufus apparently contains neurosecretory neurones, that of D. agreste is the only one equipped with a small additional retina with its own separate lens. Lens shapes vary between ovoid (A. rufus) and spherical (D. agreste). Our results demonstrate that the camera‐type eyes in A. rufus and D. agreste have optical systems that do not allow the production of a sharp image on the retina. The slugs demonstrate negative visually mediated phototactic behaviour, but no polarization sensitivity. Only one aspect of the visual environment, namely the overall distribution of light and dark, seems to be important for these slugs. As the main role of the slugs’ photoreceptors is to monitor environmental brightness and to assist the animal in orientating towards dark places, we conclude that these slugs do not need to perceive sharp images.
Keywords:retina  neurosecretion  optics  phototaxis  visual orientation  snails
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