LUMINESCENCE CONTROL IN THE TUBE-WORM CHAETOPTERUS VARIOPEDATUS: ROLE OF NERVE CORD AND PHOTOGENIC GLAND

Electrical and mechanical stimulation ofthe parapodial epidermis of Chaetopterus variopedatus evoked luminescence which was propagated only slightly to adjacent ipsilateral, but not to contralateral, parapods. In contrast, electrical stimulation of the highly modified aliform notopods led to propagation of luminescence through the entire body. Above a critical stimulus threshold, stimulation of the ventral nerve cordat any level evokedluminescencewhichwasthrough-conducted.Only stimulation of the cerebral ganglia could bring about an orderly antero-posteriorsequence of luminescence propagation. Discharges of nerve cord impulses invariably preceded the onset ofspontaneous or electricallystimulatedluminescence, and the propagation ofboth activities was interrupted by section ofthe nerve cord. Mechanical stimulation of parapods also evoked impulses at the corresponding level in the nerve cord. A large photogenic gland lying on the dorso-median surface of the 10—12th segments was refractory to electrical and mild mechanical stimulation, but responded by releasing large amounts of luminescent mucus after rupture of its epithelium. Mechanical agitation of the tube was quickly followed by the ejection of a cloud of luminescent mucus through one end, and readjustmentof the worm's position to the other end of the tube. Epitheial luminescent activities are coordinated by the ventral nerve cord and luminescent dischargesfrom the photogenic gland appearto be associated with defensive and tube cleaning activities. Irsn@RoDuCTIoN The bioluminescence of Chaetopterusvariopedatushas puzzled naturalists for more than a century because little use could be made of light emitted by an animal always confined inside its tube, which is itselflargely buried in sandy bottoms (Enders, 1909; Dahigren, 1916; Harvey, 1952). Nicol (1962) postulated that the extracellular luminescent mucus produced by the worm's epithelium could serve to repel pho tonegative intruders, such as the small crustaceans often found inside the tubes (pers. obs.). These speculations have proved difficult to test experimentallyor by field ob servationsbecause of the secretive habits of this worm. An alternativeand more tractableapproachis to make observations in the lab oratory of behavioral activities accompanying light emission and to investigate the role ofthe nervoussystem in the coordinationofluminescence. Previousinvestigators have focused on the effects of various stimuli on luminescence of “?�intact” worms (Nicol, 1952a, b, c, 1954) and of isolated notopods (Anctil, 1981), as well as the effects of putative transmitters on luminescent responses (Anctil, 1981). These studies establishedthat: (1) single and repetitiveshocks applied to the ventral nerve cord or