Bathymetric Distribution — Alvarino 
475 
Several gaps in the bathymetric distribution 
are obvious, since collections were not obtained 
at some strata. The most important sampling 
gap was in the daylight series, of about 800 m 
(1340-525 m), which interrupts the data on 
the bathymetric distribution. This lack of data, 
and the one haul from 460 m to the surface 
during the daylight series (considered only for 
the siphonophores ) , do not permit the loca- 
tion of the upper or lower limits of the dis- 
tribution of several species. 
Quantitative data were obtained by the 
method explained by Alvarino (1965 c and 
1966 ^) . 
The bathymetric zones considered are: epi- 
planktonic (upper 200 m), mesoplanktonic 
(200-1000 m), bathyplanktonic (below 1000 
m). The vertical division into zones cannot 
be static, however, because the stratification 
of the organisms is controlled by bio-physico- 
chemical factors. 
CHAETOGNATHA 
Figures 1 and 2 show the quantity of each 
of the species found and their distribution for 
the day and night series, respectively. 
The epiplanktonic species observed here 
were: Krohnitta subtilis, Pterosagitta draco, 
Sagitta bierii, S. blpunctata, S. enflata, S. 
euneritica, S. hexaptera, S. minima, S. pad pc a, 
S. pseudosenatodentata, and S. scrlppsae. A 
typical mesoplanktonic species, S. decipiens, 
also was present in the upper 100 m, but ex- 
tended to 620 m depth. 
Other species characteristic of the meso- 
planktonic levels which extended their distribu- 
tion into the bathypelagic domain were: S. 
maxima, S. macrocephala , and S. zetesios. The 
bathyplanktonic species reaching various levels 
of the mesoplanktonic zone were: Eukrohnia 
bathypelaglca, E. fowled, and E. hamata. 
During the nighttime collections, K. sub- 
tills and S. scrlppsae did not appear in the 
upper 100 m, but did appear at 500-235 rn 
and 460-235 m, respectively. S. pad flea was 
absent from any level. 
The species present in the upper 100 m 
layers for both night and daylight series, S. 
bierii, S. declplens, S. euneritica, and S. pseudo- 
senatodentata, were more abundant at night 
than during daylight, whereas S. minima was 
more abundant during the day, and the others 
appeared within the same range of abundance 
for both periods. 
The species spreading from the surface to 
300 m depth during daylight were S. euneritica 
and S. padflca, and at night, S. enflata and 
S . hexaptera , the latter appearing down to 525 
m in the daytime. 
Sagitta bierii populated the upper 100 m 
down to 500 m during both day and night, 
showing the greatest concentration in the up- 
per 100 m and the lowest between 400 and 
500 m at night, whereas during daylight the 
distribution was homogeneous along the layers 
it populated; but S. hexaptera presented the 
highest concentration from 300 to 235 m at 
night, and was homogeneous at daylight down 
to 525 m depth. K. subtilis extended during 
daylight from the surface to 525 m, with higher 
concentrations in the upper 100 m, whereas at 
night it was present only between 235 and 
500 m. 
The presence of S. declplens in the upper 
100 m both at night and by day appears to 
indicate that upwelling phenomena took place 
at this location. Two specimens of S. declplens 
were observed in the left net for the tow from 
2630 to 2210 m, and two specimens in the 
right net from 3040 to 2620 m during the 
day series. These showed evidence of con- 
tamination, however, and were omitted from 
the figures. 
S. scrlppsae extended during daylight from 
the surface to about 500 m, with maximum 
concentration at 350 to 250 m. At night it 
extended only from 235 to 460 m, with maxi- 
mum concentration between 300 and 235 m. 
The influence of light in the bathymetric 
distribution could be understood when observ- 
ing the vertical distribution of S. bierii, S. 
declplens, S. euneritica, and S. pseudoserrato- 
dentata . However, if the factor of light is re- 
sponsible for the vertical migration of these 
organisms, it fails to explain the distribution 
of K. subtilis, S. enflata, S. maxima, and S. 
scrlppsae . 
Therefore, the factors influencing the verti- 
cal distribution and displacements of the spe- 
cies of chaetognaths may be of various kinds, 
and interacting: light, temperature, oxygen, 
