72 
PACIFIC SCIENCE, Vol„ XVIII, January 1964 
cephala does not enter these waters. I examined 
the literature on the Chaetognatha of the Medi- 
terranean and the following authors did not find 
either of these species in the Mediterranean: 
Alvarino ( 1957^) , Baldasseroni (1913, 1914), 
Furnestin (1953*, b, 1955, 1956, 1957, 1958*, 
b), Ghirardelli (1950, 1952), Hamon (1952), 
Ram ult and Rose (1945), Rose and Hamon 
(1953), Scaccini and Ghirardelli (1941), Tre- 
gouboff (195 8a, b) . Ghirardelli (1950) says: 
”11 prof. Tregouboff mi segnala di aver pescato 
una sola volta un unico esemplare di E. hamata 
che disgrazatamente e andato perduto.” Rose (in 
Tregouboff and Rose 1957:482) says: "E. ha- 
mata est rarissime, elle n’a ete vue qu’une fois 
a Villefranche par M. Tregouboff . . .” and that 
"S. planctonis est tres rare et vit a grande pro- 
fondeur. Nous ne lavons jamais recoltee.” Furn- 
estin (1953^) says that certain species of chae- 
tognaths (S. hexaptera, S. setosa, S. planctonis, 
P. draco, Spadella cephaloptera, and Spadella 
profunda) were not found in the samples she 
analyzed, although they were reported by other 
authors, and she considers some of those species 
"extremement rares et d’autres demanderaient 
rneme confirmation de leur presence, comme 
c’est le cas pour S. planctonis, Spadella profunda, 
E. hamata!’ 
All this information suggests that either only 
a few individuals of S. planctonis and E. hamata 
enter the Mediterranean occasionally, which 
might happen when the outflow slows down 
and the Atlantic inflow conveys into the Medi- 
terranean stray members of the respective chae- 
tognath populations from regions in the Atlantic 
where these chaetognaths appear in the epi- 
planktonic layers; or the positive records re- 
NUMBER OF SPECIMENS OF E. homoto PER 100 M 3 WATER FILTERED 
FIG. 4. Quantitative distribution in depth of E. 
hamata in the northwest Pacific, at Station 49 of the 
Transpac Expedition (47° 35.7' N, 167° 44.8' E). 
ported are erroneous due to contamination, or 
mislabeling of the samples, or other error. E. 
hamata has been observed (Alvarino, 1957&) 
over the Iberian Atlantic continental shelf, at 
depths from 5 to 10 m, in regions of upwelling 
(author, unpublished notes), and at less than 
50 m at 46° and 47° N in the Bay of Biscay 
(author, unpublished data). 
No E. fowleri, S. macro cephala, or S. zetesios 
have been observed in the Mediterranean, and 
perhaps, according to the references above, also 
E. hamata and S. planctonis could be included 
in this group. 
The Gulf of California connects with the 
Pacific along the deep open sea, and E. hamata 
was observed there in samples taken from 700 
m depth. 
The restriction of E. bathyantarctica and S. 
marri to antarctic waters could be due to the 
fact that they inhabit the belt of great depths 
occurring in those waters (Baker, 1954), in a 
region well defined by the antarctic West Wind 
Drift. Their distribution pattern is probably re- 
lated to the circulation systems of the antarctic 
regions; thus they appear to be confined to the 
waters of the subantarctic West Wind Drift. 
2. Vertical distribution affected by the oceanic 
circulation. 
Each of the species of chaetognaths occupies 
different zones in the corresponding epi-, meso-, 
or bathyplanktonic domains. The levels each 
species occupies change somewhat under the 
effects of the geographical location, and there is 
evidence of stratification associated with size 
and maturity of the individuals, which will be 
discussed later. 
Sometimes a given species does not follow the 
normal distribution pattern, and it appears to 
assume a stratification dependent upon the pre- 
vailing currents and turbulence. In certain lo- 
calities, species typical of the upper layers are 
recorded at deeper levels than usual, apparently 
due to the sinking of the water masses they 
populate, or deep water species may appear in 
the upper layers because of upwelling. These 
phenomena are detected throughout the exam- 
ination of the chaetognath population and are 
correlated with hydrographic data (Alvarino, 
1962, in press a). 
