CHAPTER 13 

 LUMINESCENCE 



As we lift our net from the water, heavy rills of molten metal seem to 

 flow down its sides, and collect in a glowing mass at the bottom. The 

 jelly-fishes, sparkling and brilliant in the sunshine, have a still lovelier 

 light of their own at night. They send out a greenish golden light, as 

 lustrous as that of the brightest glow-worm, and on a calm summer 

 night the water, if you but dip your hand into it, breaks into shining 

 drops beneath your touch. . . . The larger acolephs bring with them a 

 dim spreading halo of light, and look like pale phantoms wandering 

 about far below the surface; the smaller ctenophores become little 

 shining spheres, while a thousand lesser creatures add their tiny lamps 

 to the illumination of the ocean. 



A. Agassiz, 1888 



PHYSICAL CHARACTERISTICS OF 

 ANIMAL LUMINESCENCE 



The production and display of luminescence are outstanding characteris- 

 tics of many marine animals. Curiously, light-production is almost un- 

 known among freshwater animals, except for a freshwater limpet and some 

 species of aquatic glow-worms (9). The light emitted is a cold light in which 

 the radiant energy is confined to the visible spectrum (400-700 m/u for 

 man). 



These blazes . . . giving more light than heat . . . you must not take for fire. 



In a few marine species which have been spectroscopically examined, the 

 luminescence has been found to present a continuous spectrum in the 

 visible range. Approximate limits of the emission spectra for several forms 

 are Aequorea forskalea and Mitrocoma cellularia (Hydromedusae), 460- 

 600 m/z; Chaetopterus variopedatus (Polychaeta), 405-605 m.ju (A max 

 465 m^); Cypridina hilgendorfii (Ostracoda), 415-620 m/*; Anomalops and 

 Photoblepharon (teleosts harbouring luminescent bacteria), 450-640 m/z. 

 The light of these various animals appears bluish. The relative spectral 

 energy distribution of the light of five marine animals is shown in Fig. 

 13.1 (15, 21,4%). 



Lights of other colours are produced by marine animals; for example, 

 Pholas, blue-green (/l max 490 m/0, ctenophores, green (A max 510 m/z), 

 polynoids, green (/ raax 515 m/z). The colour of the light may change under 

 altered conditions; e.g. the light of Pyrosoma is ordinarily bluish, but on 

 raising the temperature the colour changes to red. In the deep-sea fish 

 Echiostoma ctenobarba, a large luminescent cheek organ flashes with a blue 

 or pink light, while other minute photophores, scattered all over the body, 



536 



