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Journal of Experimental Biology 33,461-477 (1956)
Published by Company of Biologists 1956

The Eyes and the Photonegative Behaviour of Nephtys (Annelida, Polychaeta)

R. B. CLARK ¹

¹ Department of Zoology, University of Glasgow

1. The photoreceptors found in the Nephtyidae are:

(a) Two pairs of vacuolated cells lying in pigment cups, with accessory cells, embedded in the posterior part of the supra-oesophageal ganglion.

(b) One or two cells, which may or may not be vacuolated, on either side, lying a little anterior to the ganglion.

(c) Undifferentiated epidermal cells surrounded by pigment granules may be photosensitive.

2. There are both morphological and behavioural grounds for concluding that the prostomial eyes of Nephtys are homologous with the eyes of Nereis, and that they are involved in the same types of behaviour.

3. The frequency with which Nephtys swims is, within limits, a linear function of the light intensity. Although the ganglionic eyes are directional receptors the worm does not orientate itself in a light beam; presumably the light reaching them is too diffuse. In the very small species N. cornuta, the eyes are close to the surface of the brain and the worm does orientate itself in a light beam.

4. Swimming is an essential prelude to burrowing, and the brighter the light the more frequently the worm swims and the sooner it is buried. Activity in light can be inhibited by stimulating receptors on the dorsal surface of the animal by contact.