Histioteuthis is a genus of squid and the only member of the Histioteuthidae family. It goes by the common name cock-eyed squid, because in all species the right eye is normal-sized, round, blue and sunken; whereas the left eye is at least twice the diameter of the right eye, tubular, yellow-green, faces upward, and bulges out of the head.
In 2017, researchers at Duke University established that Histioteuthis uses its larger eye to see ambient sunlight, and its smaller eye to detect bioluminescence from prey animals.
The name is composed of the Greek histion (ἱστίον, "sail", a large webbed membrane between six of the arms, in some species) and teuthis ("squid").
The genus contains bioluminescent species.