Bathymetric Distribution of Chaetognaths — AlvARINO 
65 
Fig. 1 . Plan of the stations of the various expeditions in the Pacific. 
regions the number of species in the upper 200 
m exceeds the number of those in the deeper 
levels. 
DISCUSSION 
The Chaetognatha have six pelagic genera: 
Bathyspadella (recorded once, Tokioka, 1939), 
Heterokrohnia, Eukrohnia, Krohnitta, Pterosa- 
gitta, and Sagitta. The first two inhabit waters 
below the 1000 m level, Eukrohnia is mainly 
bathypelagic, with the exception of E. hamata, 
which changes its distribution in depth with 
latitude. Pterosagitta and Krohnitta populate 
the upper strata. The genus Sagitta is the most 
successful of the group: it appears to have the 
highest evolutionary level in the phylum, is the 
most abundant in species, and inhabits the 
greatest variety of environments throughout the 
oceans. Consequently, its species appear in each 
of the oceanic levels. 
The species of Chaetognatha observed by the 
author in the samples studied from the Pacific 
and Indian oceans can be grouped as follows: 
Epiplanktonic: 
Krohnitta subtilis ( Grassi ) 1881 
K. pacifica (Aida) 1897 
Pterosagitta draco ( Krohn ) 1853 
Sagitta bedoti Beraneck 1895 
