Bathymetric Distribution of Chaetognaths — Alvarino 
71 
FIG. 3. Distribution in depth of E. hamata in the Pacific, from the Bering Sea to MacMurdo Sound in the 
Antarctic. 
both poles (Fig. 3). This diagram is very similar 
to that of Thiel (1938) for the same species, 
covering from 60° S to 20° N in the Atlantic. 
This schematic diagram showing the distribu- 
tion of E. hamata in the Pacific from arctic to 
antarctic waters was made by combining the 
data obtained from the study of more than 4,000 
samples taken by the Scripps Expeditions in the 
Pacific from 1952 to 1962 (Fig. 1), and the 
monthly CalCOFI cruises for 1954 and 1958. 
It is important to notice in the present diagram 
the incipient emergence of E . hamata in the 
equatorial region. This emergence was also 
found for E. fowleri and S. maxima; while S. 
bipunctata occasionally submerged slightly in 
some locations of this region. For example, at 
station 49 of the Transpacific Expedition (47° 
35.7' N- — 167° 44.8' E), the maximum number 
of individuals of E. hamata was found at about 
225 m depth (Figs. 4, 5). In this locality the 
number of specimens or the volume of chae- 
tognaths will be larger at this depth than at 
any other layer in this column of water, al- 
though the chaetognath population is repre- 
sented by only one species. However, if these 
data were combined with the data from several 
other localities, the large amount of specimens 
at this layer will be shown in the results. This 
may be the case in Leavitt’s ( 1947 ) surprising 
results. 
S. maxima follows a pattern rather similar to 
E. hamata in its respective vertical distribution 
in the Pacific; it was observed in the present 
studies from 45° N to 46° S, although it reaches 
levels below those occupied by E. hamata in 
both high latitudes. S. maxima was observed 20 
times in California waters, at about 140 m 
depth, in regions where upwelling was evident. 
However, it is found in these waters normally 
at depths below 140 m (author, unpublished 
data ) . 
The adjacent seas isolated from the depths of 
the ocean by shallow regions do not have repre- 
sentatives of the bathyplanktonic species. E. 
hamata is recorded along the narrow Aleutian 
passes that connect the Bering Sea with the 
Pacific, as this species extends into the surface 
layers in that region. However, in other areas, 
where the population of E. hamata does not 
inhabit the upper strata and the connecting sill 
with neighboring waters is above its vertical 
distribution level, it does not pass to adjacent 
seas. This could be the case in the Mediterra- 
nean, where the Gibraltar sill at a depth of 320 
m and the outward undercurrent make a barrier 
to the inward migration of the chaetognaths 
which in those latitudes inhabit layers below the 
threshold. A similar picture was found for the 
Siphonophorae (Bigelow and Sears, 1936); for 
the deep water Medusae ( Kramp, 1924), and 
for the euphausiids (Ruud, 1936). Germain 
and Joubin (1916) reported E. hamata and S. 
planctonis from six and four localities respec- 
tively in the Mediterranean. Germain ( 1930— 
1932) includes E. hamata in the fauna list of 
the Mediterranean and explains that S. macro- 
