THE DISTRIBUTION OF THE CHAETOGNATHA 

 OF THE SOUTHERN OCEAN 



A 



By p. M. David 

 (Plate X; Figs. 1-13) 



INTRODUCTION 



NUMBER of reports on antarctic Chaetognatha have been already published (Steinhaus, 1900; 

 Fowler, 1907; Ritter-Zahony, 1909, 191 1; Germain, 1913; Jameson, 1914; Johnston and Taylor, 

 1921; Burfield, 1930; Bollmann, 1934; Thiel, 1938; Ghirardelli, 1953), butin most cases the collections 

 reported on were small and restricted both in horizontal and in seasonal range. 



The Discovery collections cover nearly all areas of the Southern Ocean in all seasons of the year, and 

 from this material it is possible not only to compile a complete list of species present, but also to 

 discover quite a lot about their distribution and something of their life histories. The approach to the 

 subject adopted here is essentially distributional rather than systematic. 



While working on Sagitta gazellae I also assembled data on the other species in the collections, and 

 was struck by the very consistent pattern of vertical distribution of the commoner chaetognath species. 

 This pattern was not clearly demonstrated in the earlier reports on antarctic chaetognaths, and it 

 seemed worth while to attempt to show it in the present paper. 



Throughout this paper the name ' Southern Ocean ' has been employed to describe all that ocean 

 which lies between the subtropical convergence and the Antarctic continent. This area is divided into 

 two zones, the subantarctic and the antarctic, which are separated by the antarctic convergence. While 

 it has been held by some authorities that the Southern Ocean is not a geographical entity, there is no 

 doubt that it has at least a faunistic unity and is therefore a term of considerable value to those working 

 on the distribution of animals in the southern hemisphere. 



ACKNOWLEDGEMENTS 



I am greatly indebted to Mr J. W. S. Marr for advice and for the loan of his notes on chaetognaths 

 from the second and fourth commissions of Discovery II (193 1-3 and 1935-7). These have enabled 

 me to check many points arising from the work and have considerably lightened the task of searching 

 through the collections for stray exotic species. I am also grateful to Mr A. Styles for preparing the 

 diagrams for publication. 



MATERIAL AND METHODS 



All the material used for this study has been taken from the collections made by ships of the Discovery 

 Committee and subsequently of the National Institute of Oceanography. It would, of course, be best 

 if all the chaetognaths in the collections could be used for this work, but the immense labour involved 

 in sorting and identifying them from the large number of samples available would not be repaid by 

 the results, and therefore an attempt has been made to manage on a limited number of stations chosen 

 from many radiating lines and many other scattered stations. For a start it was desirable to find a line 

 of stations which extended from the subtropics southwards to as near the Antarctic continent as the 

 ice conditions would permit. The line chosen was that worked in March 1937 on the Greenwich 

 meridian (0°) (see Fig. i). This gives a close approximation to typical summer conditions. In order to 



