Y. HAXEDA 349 



results. Microscopic examination did not reveal any luminous bac- 

 teria. On blotting paper the luminosity of the luminous mucus faded 

 out after a few minutes while the paper was drying, but dropping 

 water on the blotting paper revived the luminosity. The color of the 

 light of luminous mucus on the blotting paper was pale blue, which 

 changed to yellowish when the paper was rubbed. The intensity of 

 luminosity was also increased by rubbing. 



Mollusca Except Cephalopoda 



Luminous species of the great group of Mollusca, excluding squids, 

 are comparatively rare. Seven genera of Gastropoda, Phillirrhoe, 

 Tethys, Kaloplocamiis, Plocamophorns, Latia, Dijakia, and Tonrui, 

 are known to be luminous. Two genera of Pelecypoda, Pholas and 

 RoceUaria, are also known to be luminous. 



In Japan the luminous species of Gastropoda, Opisthobranchiata or 

 sea slugs, in which the shell is absent, were studied by a number of 

 workers. Dr. Okada and Dr. Baba observed luminous sea slugs, 

 Plocamophorus tilesii, in Mutsu Bay. The mucous cells were scattered 

 over the whole body, and the luminous slime came out of mucous 

 cells. 



Beautifully colored plates of two luminous sea slugs, namely Ploca- 

 mophorus tilesii and Plocamophorus imperialis, were reproduced in 

 the book Opisfhohranchia of Sagami Bay collected by His Majesty, the 

 Emperor of Japan (1949). The beautifully colored large sea slug, 

 Calinga ornata, found in Japanese waters, is also known to be lumi- 

 nous. Recently Kato (1949a and b) reported the luminosity of the 

 small sea slug, Kaloplocamiis ramosum, which comes from the east 

 coast of Japan. The animal has many luminous cells and no pores, 

 but the luminous cells contain large granules. It emits intermittently 

 bluish Hashes of light when irritated but it discharges no secretion 

 into the water, although other luminous sea slugs are known to do so. 

 I have observed it in the dark at the beach of Usa Marine Biological 

 Station of Kochi University in November, 1953, and have tested for 

 the luciferin-luciferase and ATP reactions, with negative results. The 

 famous transparent pelagic nudibranch Pliyllirrhoe bucephala is occa- 

 sionally collected in the neighborhood of the Misaki Marine Biological 

 Station. 



