Function of the Dimorphic Eyes in the Midwater Squid Histioteuthis dofleini

Abstract

The squid Histioteuthis dofleini, like other members of the family Histioteuthidae, has a large left eye and a small right eye. The large eye points in a dorsal posterior direction while the squid typically orients at an oblique angle with the arms downward. The large eye, as a result, points vertically upward. The small eye appears to be directed ventrolaterally. This squid occurs primarily at depths of 500 to 700 m during the day where it is exposed to low levels of downwelling light. Presumably the large eye utilizes this faint downwelling light while the smaller eye utilizes bioluminescent light.