Six spectral sensitivity classes in crab visual interneurons

Summary Electrophysiological determination of the spectral sensitivity of units from the retina, optic lobes and brain of the crabParagrapsus gaimardii revealed six major colour types. Single peaks occurred in the UV, blue-green, green and yellow, and further units showed either a broad-band sensitivity or double peaks in the violet and yellow.Many of the curves had broad shoulders and offset peaks, markedly different in shape to curves suggested by Dartnall for rhodopsins with the same peak values, but similar to those previously recorded for other crabs. This finding, allied with limited evidence that a number of the colour types changed one from the other depending on illumination level, suggests that at least some of the colour types may result from a filtering of the light reaching a single retinal type.The UV sensitivity, recorded from brain interneurons, is the highest so far found in crabs.The range of colour types recorded provides a good potential substrate for colour vision. It is therefore of interest that a survey of a total of 105 units provided no evidence for colour opponency.Queen Elizabeth II Fellow in Marine Science, 1978–1979