Tetraplatia — Hand 
339 
north, Leloup obtained three specimens of T. 
volitans from the "Meteor” samples. From 
these facts it would not seem unreasonable 
to suggest again that T. chuni may be an 
aberrant specimen of T. volitans . 
Among the many plankton samples ex- 
amined I had the good fortune to discover 
specimens of Tetraplatia in a group of samples 
from horizontal, closing-net, tows taken in a 
vertical series. Four series of samples were 
taken at a single station (approximate posi- 
tion, 33° N., 117° W.) on the 4th and 5th of 
March, 1953. These consisted of two night 
series (2000-0330 hrs., 0400-0515 hrs. P.S.T.; 
the first series of 12 separate tows and the 
second series of only four separate tows) and 
two daylight series (1620-1820 hrs., 0615- 
1100 hrs. P.S.T.; the first of five tows and the 
second 11 tows). These tows were made with 
a net 1 meter in diameter, towed for 10 min- 
utes. Table 1 indicates the length of wire used 
in each of the tows and the numbers of 
Tetraplatia volitans taken. 
From the table it can seen that Tetraplatia 
was common in the first night series of sam- 
ples and was absent from all others. These 
results agree very well with the suggestion 
of Leloup (1935) that Tetraplatia undergoes a 
diurnal vertical migration, approaching the 
surface only at night, except for the absence 
of specimens from the second night series. 
Sunrise, on the days when these samples were 
taken, was at approximately 0625 P.S.T. and 
during the time when the second series of 
night samples were taken the moon was 
slightly more than half illuminated and was 
nearly overhead. In the first night series no 
specimens were taken at the surface or at 10 
meters depth while two and seven specimens 
were taken at 25 and 40 meters, respectively, 
so perhaps Tetraplatia was really absent from 
only the latter two hauls of the second night 
series. Also, since these latter two hauls were 
taken one hour and 45 minutes and one hqur 
and 15 minutes, respectively before sunrise, 
it may well be that the Tetraplatia had already 
TABLE 1 
The Number of Tetraplatia volitans Taken in a 
Vertical Series of Horizontal Closing-Net Tows 
March 4 and 5, 1953 
LENGTH OF 
WIRE OUT 
(meters) 
NJGHT SERIES 
DAYLIGHT SERIES 
No. 1 
No. 2 
No. 1 
No. 2 
Surface 
0 
0 
0 
0 
10 
0 
0 
0 
0 
25 
2 
0 
0 
0 
40 
1 
0 
0 
0 
60 
4 
** 
** 
0 
80 
3 
** 
** 
0 
100 
2 
** 
* 
0 
150 
0 
** 
** 
0 
200 
1 
** 
** 
* 
300 
0 
** 
** 
* 
400 
** 
** 
* 
* Net did not function properly. 
** No sample taken. 
begun their descent toward their daytime 
environment. 
Excluding the 19 specimens collected in 
the series of hauls just reported, a total of 
134 specimens has been recovered from 45 
net hauls and of the 45 net hauls, only 12 
were made during daylight hours. Of these 
12 daylight samples, all but one were tows 
during which the net fished at depths greater 
than 300 meters, the exception being a tow 
whose greatest depth fished was approxi- 
mately 70 meters. As compared to this single 
daylight haul which captured a single spec- 
imen, 15 night net hauls whose greatest depth 
reached was 70 meters produced a total of 19 
specimens. The 11 remaining daylight tows 
which fished to depths greater than 300 meters 
produced a total of 79 specimens (1, 1, 1, 1, 
2, 3, 7, 11, 16, 17 and 19 specimens per haul, 
respectively) . With the exception of the haul 
which produced 16 specimens, these hauls 
were tows which fished from about 500 meters 
to 1,022 meters. The sample containing 16 
specimens was a closing net tow taken at a 
depth of about 300 meters at 1455 P.S.T. 
From the data presented above it now seems 
to be apparent that Tetraplatia volitans is a 
