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Holding Mirrors up to Nature: The Structure, Function, and Evolution of the Eyes of Scallops

Daniel Speiser, University of South Carolina

15 September 2017

The eyes of animals come in a variety of forms and some of the most unusual designs are found in certain types of mollusks. Scallops, for example, have dozens of eyes arrayed along the edges of their valves. These are among the only eyes known to use a concave mirror to focus light for image-formation, they are one of the very types of eyes to contain two separate retinas, and they provide scallops with visual acuity that far exceeds that which is observed in other bivalves. Dr. Speiser will present new evidence that the eyes of scallops are dynamic structures that demonstrate a light-evoked pupillary response and may be able to change shape voluntarily in ways that influence the qualities of the images that fall on the two separate retinas. Second, he will discuss the range of visually-influenced behaviors demonstrated by scallops, some of which are quite dramatic because scallops – unlike other bivalves – are able to swim for short distances using a form of jet-propulsion. Third, Dr. Speiser will review evidence that the scallop nervous system is complex and centralized relative that which is observed in other bivalves and that the optic nerves traveling from the dozens of image-forming eyes on the mantle may project to the lateral lobes of the parietovisceral ganglion (PVG) in a spatiotopic manner. These considerations will build to a discussion of how scallops and their relatives may be useful for studying the co-evolution of sensory structures, forms of locomotion, and centralized nervous systems.