Cuttlefish have a uniquely shaped pupil comprising several slits in different orientations - some are W-shaped and others, like S. apama, have one horizontal slit that bends obliquely vertical. Light entering the eye is controlled by altering the shape of the entire eyeball. To focus on nearby objects a cuttlefish contracts a surrounding layer of the muscle, moving the lens forward, away from the retina and it focuses on distant objects by drawing the lens in. Cuttlefish are known to be color-blind, having only one visual pigment at 492nm. Despite being color-blind cuttlefish are very good at blending into colorful natural environments (at least in shallow depths of water).
Marshall, N. J. and J. B. Messenger. 1996. Colour-blindcamouflage. Nature 382: 408–409
Mathger, L., A. Barbosa, S. Miner and R. T. Hanlon. 2006. Color blindness and contrast perception in cuttlefish (Sepia officinalis) determined by a visual sensorimotor assay. Vision Res. 46: 1746-1753.
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