Experimental studies on the light sense in the hagfish,Eptatretus burgeri andParamyxine atami (Cyclostomata)

Photo-reception and sensitivity to light were studied in two Japanese hagfishes,Eptatretus burgeri living in shallow water andParamyxine atami living in water of about 100m depth. Both species responded to general illumination by first moving the tail or head and then by swimming. Local illumination revealed that regions most sensitive to light were the skin of the tail in both species and a line of unpigmented skin running down the back ofE. burgeri. The light sensitivity of the lensless eyes, which are situated below the skin, was very weak in both species.P. atami showed shorter reaction time to light thanE. burgeri. No change in skin colour was induced either by almost complete hypophysectomy or by continuous illumination against a white background. Under-water observations with SCUBA revealed that free movingE. burgeri responded well to illumination uncovered during the night, but the ones buried in mud, with only the heads uncovered did not.