Tiny and transparent, the marine crustacean Paraphronima gracilis sees the world through two large eyes that envelop its head like a high-tech space helmet. Now, a new study of this amphipod—a close relative of the sand hopper—reveals that it has 32 different retinas, the light-sensitive parts of its eyes. “We have never seen the retina split up this way in any other arthropod eye, not in insects, not in crustaceans, or other animals with a compound eye,” explains Jamie Baldwin Fergus (http://invertebrates.si.edu/baldwin-fergus.htm), Ph.D., Peter Buck Postdoctoral Fellow at the Smithsonian’s National Museum of Natural History, and lead author of a detailed study of this eye published online on January 15, 2015 in Current Biology. “This eye design has not been described previously and its function is unknown,” said Dr. Fergus. In addition to Dr. Fergus, Karen Osborn (http://invertebrates.si.edu/staff/osborn.cfm), Ph.D., of the Smithsonian’s National Museum of Natural History, and Sonke Johnsen (http://sites.biology.duke.edu/johnsenlab/), Ph.D., of Duke University are also co-authors of the Current Biology paper. Living at depths of 150 to 500 meters off the coast of California, P. gracilis inhabits an environment that is totally dark to the human eye. As it swims, its eyes are positioned upward, looking for prey, transparent creatures called siphonophores, swimming above. In most compound eyes, the retina is a single continuous pigmented sheet. The 32 retinas in the eyes of P. gracilis appear as a series of tiny orange upside-down pyramids neatly arranged in two rows on either side of the animal’s head. Light travels to each retina through a row of transparent facets called ommatidia that cover the eye, collecting light that is channeled through guide tissue similar to fiber optic cables.
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