Spectral Sensitivity of the Scallop Pecten maximus.

The spectral sensitivity of the scallop Pecten maximus was determined behavorially; the shadow reflex was used as the index of sensitivity. The photopic visibility curve displays two prominent peaks, one at approximately 480 mmicro, and the other with wavelength maximum at approximately 540 mmicro. Reduction of background illumination results in a great increase in sensitivity at 480 mmicro relative to the 540-mmicro peak. This suggests that the scallop may possess photoreceptors that behave like rods in vertebrates. sensitivity of this animal.