Dim light vision of Squilla mantis L

¹ Zoological Station, Naples, Italy

The anatomy of the eye of Squilla mantis and the geometrical optics derived from it are briefly described. The shape and size of the electroretinogram (ERG) are dependent on a) position where it is picked up, b) the light intensity, and c) the change of intensity. Single-fiber analysis confirms the results obtained by the anatomy and the ERG of the eye. Frequency of response of a single secondary fiber to intensity changes of light is proportional to the derivate dI/dt (I = intensity; t = time). The Squilla sees a moving object as the sum of the intensity changes caused by that object, varied in time and space. The eyes have a maximum of sensitivity for light of 535–555 mµ wavelength, and a second maximum in the near ultraviolet light, the latter partly seen as green fluorescence due to an eye pigment. Anatomy, physiology, and the environmental conditions have been combined to explain the vision of this animal, adapted to his life in the blue-violet twilight of the deeper Mediterranean sea.

Key Words: twilight vision • arthropod eye histology • compound eye • geometrical optics • arthropod EEG • single-fiber • response in compound eye to different wavelengths, UV, polarized light • frequency change with intensity, change with time • single-fiber response to moving fish • summation of light in an apposition eye

Submitted on April 25, 1963