Transitory Eye Shapes and the Vertical Distribution of Two Midwater Squids

Abstract

In two cranchiid squids, Sandalops melancholicus and Taonius pavo, the shapes of the eyes change with growth. Compressed eyes with ocular appendages occur in the larvae living in the upper few hundred meters of the ocean. Tubular eyes occur in juveniles that live within a depth zone between about 400 and 700 m. Nearly hemispherical eyes are found in adults living at depths greater than 700 m. The shapes of the compressed and tubular eyes offer strong countershading advantages to squids living at depths where downwelling light is important in prey-predator relationships.