Photophore and Eye Movement in the Euphausiid Meganyctiphanes norvegica (G. O. Sars)

Abstract

THE complex structure of the light-emitting organs of euphausiids has long been known^1,2, though their precise function has eluded investigators. While examining further this problem, it has become clear that these organs, all of which are movable except those on the eye-stalks, do not operate independently but may be co-ordinated. Meganyctiphaneshas 10 photophores, one incorporated in the eye-stalk below each eye, 4 in the thoracic region at the bases of the 2nd and 7th pairs of appendages, and one between each of the first 4 pairs of pleopods. The eye-stalks, bearing the large compound eyes and photophores, project laterally and are closely approximated at their base in such a way that the eyes, though they may be moved independently to some extent, may be turned together in the sagittal plane, the amount of possible rotation being greater than 90°. The thoracic and abdominal photophores can turn through nearly 180° to face forwards, ventrally, or backwards.