Spatial Resolution Determined by Electrophysiological Measurement of Acceptance Angle in two Species of Benthic Decapod Crustacean

Abstract

Angular sensitivity functions were determined electrophysiologically for retinula cells in Nephrops norvegicus and Munida rugosa. For such aquatic species it is shown that reliable measurements cannot be obtained unless the eyes are submerged. In both cases, for submerged eyes, there is a significant reduction in retinula cell acceptance angles with light adaptation. In N. norvegicus the change is from 11·3° dark adapted (DA) to 8·85° light adapted (LA). In M. rugosa there is a larger difference, 12·5° (DA)–6·58° (LA). The changes in acceptance angle with adaptational state can be attributed to differences in screening pigment position between light- and dark-adapted eyes. In N. norvegicus only the retinula cell proximal pigment is migratory. The small change in acceptance angle with adaptation is consistent with the fact that the eye uses superposition optics even when light-adapted.