Marine Snails — Haneda 
153 
to Mr. Y. Shinoda and Mrs. S. Nunes, for 
their assistance in collecting materials during 
my stay in Hawaii; to Mr. H. B. Summers, for 
having assisted me in the preparation of the 
manuscript; and to Mr. H. Okuyama of Naka- 
nogoh Primary School of Hachijo Island who 
assisted in collecting materials, and whose 
keen observations made this discovery of 
luminescence in Planaxis possible. 
I would also like to express my warmest 
appreciation to the Committee of the Lumi- 
nescence Conference, for inviting me to par- 
ticipate in the meetings of March 29-April 1, 
1954 at Pacific Grove, California, which gave 
me the opportunity to collect many American 
specimens. 
MATERIALS 
The luminous marine snails which I have 
collected all belong to the genus Planaxis of 
the Planaxidae and are comparatively small. 
The various species of this genus in which I 
have observed luminescence are shown in 
Table 1. 
AH of these animals are capable of living 
in aquaria for a long time, usually up to two 
to three months, and in some cases as long 
as one year. I collected many specimens in 
April at Hachijo Island and brought them to 
Fig. 1. Planaxis virgatus. 
Fig. 2. P. labiosus. 
my laboratory in a small bottle. These animals 
lived in a small dish until the end of August 
of the same year, during which period the 
water was changed several times. I twice air 
mailed several living specimens of Planaxis 
virgatus in a small bottle of sea water to Dr. 
E. N. Harvey of Princeton University. The 
first time all the specimens were dead when 
Dr. Harvey received them. But the second 
time the specimens arrived alive. 
I brought some specimens of the Hawaiian 
species in a small bottle of sea water to the 
Conference on Luminescence and demon- 
strated their luminosity to Dr. Harvey and 
other members present. Afterward I took 
those specimens on my journey in the United 
States and brought them back to my labora- 
tory about two months later. The snails lived 
in a small aquarium until March 21, 1955, and 
some of them hatched larvae, but luminosity 
in these larvae was not observed. 
OBSERVATION OF LUMINOUS PHENOMENA 
Under natural conditions, the light of these 
animals cannot be seen well; they will emit 
light only under strong stimulation. If many 
specimens are placed in a bottle and are well 
shaken in the dark, some of them become 
luminous and twinkling. The light usually 
continues one or two minutes after stimula- 
tion, then gradually disappears. But if the 
body of the snails is irritated, the light re- 
