A Possible Function of the Iris Groove of Nautilus

Abstract

The eye of Nautilus has no lens or cornea. The interior of the eye is apparently in direct communication with the surrounding water by way of the open pupil. Running ventrally from the pupil, on the outside of the iris, is a groove. The groove is wide and shallow immediately beneath the pupil and becomes deeper toward the ventral edge of the iris (Fig. 1). It is lined with ciliated epithelium (Muntz and Raj, 1984). In 1865, Hensen suggested that the function of the groove might be to direct a current of water across the pupil, to prevent foreign objects from entering the eye. The observations reported in this chapter suggest that the iris groove may indeed provide some protection for the eye, though not in the manner suggested by Hensen.