Spatial vision in the prosobranch gastropod ampularia sp

The eyes of gastropods of the genus Ampularia superficially resemble the well-developed camera-type eyes of Littorina littorea and Strombus raninus. The eyes are of the closed-vesicle type, having a cornea and a lens that is separated from the retina by a narrow vitreous body. Light and electron microscopy were used to generate an accurate geometrical model of the Ampularia sp. eye, which was then used to predict its optical performance. The image quality of the lens was investigated using a modified microscope and revealed that images suffer from severe aberrations. The focal length was estimated to be approximately 430 microm, putting the plane of best focus in or just proximal to the rhabdoms. The aberrant optics result in a large retinal blur-circle with a diameter of approximately 120 microm and an angular half-width of approximately 17 degrees, allowing only comparatively poor resolution compared with the eyes of Littorina littorea and Strombus raninus. Behavioural experiments revealed no significant optomotor response. The results imply that Ampularia sp. has poor spatial vision, limited by the blur-circles on the retina. The eyes appear to be suitable only for relatively simple visual tasks, such as finding an open water surface for breathing, but the large size of the eye allows it to perform this task even at night.