A SHORT-WAVELENGTH PHOTORECEPTOR CLASS IN A DEEP-SEA SHRIMP

In the world of midwater, mesopelagic animals, downwelling sunlight is filtered by the overlying water to a limited waveband centered near 4 75 nm. Consequently, the visual pigments of most of these species abso rb maximally between 450 and 500 nm. The only exceptions occur in some fishes, which have additional visual pigments absorbing at long wavel engths (550-580 nm) matched to their red bioluminescence. We now find that the mesopelagic decapod shrimp Systellaspis debilis has two visua l pigments. One of these absorbs maximally in the expected range (lamb da(max) = 498 nm), but the other is maximally sensitive at very short wavelengths, approaching the near-ultraviolet (lambda(max) = 410 nm). The discovery of a visual receptor class absorbing at such short wavel engths in a mesopelagic animal suggests that visual systems in the dee p sea may be far more diverse, and potentially more complex, than prev iously suspected.