Fig. 6

Double, superposition compound eyes found in some deep-sea euphausiid crustaceans (better known as ‘krill’). The euphausiids are one of the few crustacean groups containing refracting superposition eyes, with optics similar to the schematic in Fig. 2b. The eyes shown here are rather unusual in that the dorsal half is arrayed so as to inspect just the downwelling light arriving from the ocean above, while the ventral half forms a nearly complete spherical array sampling in all other directions. These eyes are thus superposition analogues of the fiber-optic eye type illustrated in Fig. 4c. a, b Light-microscopic views of the double eye of Nematobrachion boöpis (photographs by T. Frank, Harbor Branch Oceanographic Institution). c Scanning electron micrograph of one double eye of Nematoscelis sp. This eye has become somewhat distorted during the preparation for imaging. The upper flattened array and the lower spherical array are easily distinguished (photograph by D. Pales)