578 THE BIOLOGY OF MARINE ANIMALS 



Finally, there is the significance of luminescence as a means of recogni- 

 tion between members of a species. The best-authenticated case among 

 marine animals is that of the polychaete Odontosyllis, in which both sexes 

 luminesce during spawning. Members of this species exhibit well-marked 

 lunar periodicity, and swarm in surface waters about an hour after sunset 

 on the second, third and fourth days after full moon. The female displays 

 a bright continuous glow lasting 10-20 sec while the male flashes inter- 

 mittently. During the spawning process the female swims about rapidly 

 in small circles near the surface and becomes brightly luminous. The males 

 approach obliquely upwards from deeper water and make for the centre 

 of the luminous ring. Both sexes then shed their gametes into the water. 

 If the male worm fails to reach the female before her light fades, he 

 hesitates until she becomes luminescent again, and then re-approaches her 

 to complete the spawning act. 



Certain oegopsid squid and teleosts have well-defined photophore- 

 patterns which could serve as intraspecific recognition signals. The many 

 species of myctophid fish differ in the number and arrangement of light- 

 organs. Squids differ not only in the quantitative arrangement of their 

 photophores, but in the colour of the light emitted as well. In Watasenia 

 there are also differences in the photophores of the two sexes. Harvey 

 suggests that luminescence in this last species may be a means of attraction 

 between the sexes during the spring migration to the surface. Since both 

 squid and fish school, the photophores may aid in holding the shoal 

 together. There is suggestive evidence that the photophores of deep-sea 

 shrimp may be of assistance in swarming (19). Certain bathypelagic tele- 

 osts of the family Melanostomiatidae also show sexual differences in the 

 structure and colours of their luminescent barbels, and these differences 

 may have behavioural significance (2, 38). 



REFERENCES 



1. Alcock, A., A Naturalist in Indian Seas (London, John Murray, 1902). 



2. Beebe, W. and Crane, J., "Deep-sea fishes of the Bermuda oceanographic 

 expeditions. Family Melanostomiatidae," Zoologica, N.Y., 24, 65 (1939). 



3. Beebe, W. and Crane, J., "Eastern Pacific expeditions of the N.Y. Zoo- 

 logical Society. 37. Deep-sea ceratioid fishes," ibid., 31, 151 (1947). 



4. Bertelsen, E., "The ceratioid fishes," Dana-Rept. No. 39, 276 pp. (1951). 



5. Bonhomme, C, "Recherches sur l'histologie de Tappareil lumineux des 

 Polynoiines," Bull. Inst. Oceanogr. Monaco, No. 803, 8 pp. (1942). 



6. Bonhomme, C, "L'appareil lumineux de Chaetopterus variopedatus Clap. 

 Recherches histologiques," ibid., No. 843, 7 pp. (1943). 



7. Bonhomme, C, "La luminescence de Heterocirrus bioculatus Keferstein," 

 ibid., No. 871, 7 pp. (1944). 



8. Bonhomme, C, "Sur un mode particular d'elimination des produits photo- 

 genes chez Poly cirrus caliendrum Clap, et Poly cirrus aurantiacus Grube," 

 Bull. Soc. Zool. Fr. y 11, 341 (1953). 



9. Bowden, B. J., "Some observations on a luminescent fresh-water limpet 

 from New Zealand," Biol. Bull., 99, 373 (1950). 



