70 
PACIFIC SCIENCE, VoL XVIII, January 1964 
Shellback, Monsoon, Capricorn, Downwind, 
Troll, Tethys.) 
The bathyplanktonic domain is populated by 
E. fowleri, E. bathyantarctica, E. bathypelagica, 
H. mirabilis, and B. edentata. 
Some species, such as E. hamata, E. fowleri, 
E. bathypelagica, H. mirabilis, S. maxima, and 
S. macrocephala, are common to both the arctic- 
subarctic and antarctic-subantarctic waters. They 
are cosmopolitan in the most complete sense, 
with the exception of E. bathypelagica, connect- 
ing both polar or subpolar regions along the 
depths of the oceans. Thus, the isolation of the 
arctic and antarctic is relative (Barnes, 1957). 
E. hamata populates the Atlantic, Pacific, and 
Indian oceans at different depths, and the upper 
layers of the arctic and antarctic (various authors 
and personal unpublished data ) . E. fowleri also 
inhabits the three oceans, extending in the Pa- 
cific from 55° 57' N to 46° S (several authors, 
and personal unpublished notes). E. bathype- 
lagica (personal studies) extends in the Pacific 
from 53° 56' N to 46° S. H. mirabilis, reported 
by Bieri (1959), David (1958 b), Ritter-Zahony 
(1911), and Tchindonova (1955), was observed 
in samples taken respectively from 2300 m, 
3000-2000 m, 2000-3423 m, and 5000 m. S. 
macrocephala (personal records) appeared in 
the Pacific from 40° N to 46° S. S. maxima was 
observed in the present material from 45° N 
to 46° S. However, observations obtained up 
to the present show that the antarctic and sub- 
antarctic waters have three indigenous chaetog- 
naths: S. gazellae in the upper layers, and E. 
bathyantarctica and S. marri in deep waters. The 
antarctic belt also has indigenous siphonophores: 
Diphyes antarctica, Manus antarcticus, and Py- 
rostephos vanhoeffeni, and one species, Dimo- 
phyes arctica, which is common to the arctic 
and antarctic waters, extending to deep levels 
at low latitudes (author, unpublished data). 
The arctic-subarctic region has S. elegans as a 
chaetognath of its own, and no siphonophore 
restricted exclusively to this region. 
In the Pacific from 40° N to 40° S at least 
20 species of oceanic Chaetognatha are present 
in the upper 200 m. In this same span, two 
other species of Sagitta are found at depths 
below the 200 m level: S. decipiens, extending 
from 200 or 600 m deep; and S. zetesios, from 
300 to 800 m, besides the other species that 
cover the same span but extend both northward 
observed for both species in the Atlantic and 
Indian oceans (author, unpublished data). 
The mesoplanktonic domain can be subdi- 
vided into three zones: upper, median, and low, 
each having its characteristic species. The indi- 
cations are that each species may have its own 
vertical range, a region in which to find optimal 
conditions. The zonation in the strata varies, 
not only for the different species but also for 
the respective individuals at different stages of 
maturity. The type of distribution for some ? 
species may vary with latitude, season, etc. Thus 
it is necessary to emphasize that the above 
established classification must be further sub- 
divided into other types of vertical stratification 
or zonations. These are: 
1. Vertical distribution related to latitude. 
2. Vertical distribution affected by the cir- 
culation in the oceans. 
3. Ontogenic vertical distribution. 
4. Seasonal and diurnal vertical distribu- 
tion. 
With the exception of zonation in relation 
to seasonal or diurnal migration, a problem that 
merits special attention in another study, these 
points will now be discussed. 
1. Variations in the vertical distribution in re- 
lation to latitude. 
The sampling at different depths unfortu- 
nately does not cover the Pacific conveniently. 
Although in most of the cases the plankton 
samples were taken at different depths in each 
of the stations distributed throughout the Pa- 
cific (Fig. 1), in only half of the cases were 
the stratified samples taken with closing nets. 
However, with the data at hand it could be 
observed that the distribution in depth varies 
for some species with the geographical location. 
Species that appear only in deep layers in one 
region, are found in shallower depths or in 
surface waters in other areas. 
E. hamata is unique in this respect; it covers 
the epi-, meso-, or bathyplanktonic categories 
in relation to latitude. It lives at great depths 
in the tropical and subtropical regions of the 
oceans, but in the subarctic and subantarctic 
regions it gradually rises near the surface toward 
