Figure 7.

Variation in thickness of the screening pigment layer in squid. Differentials of screening pigment density and movement are relating to their living light conditions. In contrast to coastal squid which possess dense and dynamic moving screening pigments to avoid bright sunlight, absence of screening pigment in mid-water squid maximize the amount of light reaching the retina. (A) A sample of dynamic movements of screening pigment granules in a coastal squid (S. lessoniana). L indicates the light-adapted retina; D as the dark-adapted retina. (B) A sample of absence of screening pigment movement in deep-sea squid (A. falco). Scale bars: 10 μm. (C) Varieties of thickness of the screening pigment layer at the ventral retina of the dark-adapted specimens. Black bars represent the thickness of the screening pigment layer in percentage relative to the length of the rhabdomeric layer.