A novel eye in 'eyeless' shrimp from hydrothermal vents of the Mid-Atlantic Ridge

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Abstract
Rimicaris exoculata1 is a shrimp that swarms over high-temperature (350 °C) sulphide chimneys at Mid-Atlantic Ridge hydrothermal fields (3,600 m)1–7. This shrimp lacks an externally differentiated eye1, having instead a pair of large organs within the cephalothorax immediately beneath the dorsal surface of the transparent carapace, connected by large nerve tracts to the supraesophageal ganglion. These organs contain a visual pigment with an absorption spectrum characteristic of rhodopsin. Ultra-structural evidence for degraded rhabdomeral material suggests the presence of photoreceptors. No image-forming optics are associated with the organs. We interpret these organs as being eyes adapted for detection of low-level illumination and suggest that they evolved in response to a source of radiation associated with the environment of hydrothermal vents.