SPECTRAL SENSITIVITY OF THE CHAETOGNATH<i>SAGITTA HISPIDA</i>CONANT

Abstract

Using phototaxis as a behavioral measure of photosensitivity, the spectral sensitivity of Sagitta hispida Conant (Chaetognatha) was determined. S. hispida is most sensitive to blue-green light, with maximum sensitivity at 500 nm. From 400-580 nm, the shape of the action spectrum for phototaxis approximates an absorbance spectrum for a rhodspin-based visual pigment. This suggests that photoreception is mediated largely by a single major pigment. An accessory pigment may play a role in photo-reception at longer wavelengths. S. hispida is adapted for greatest photosensitivity wherever blue-green light dominates the available spectrum. This finding is consistent with the geographical range of this species, which comprises relatively clear blue-green tropical and subtropical seas.