2I 8 DISCOVERY REPORTS 



(c) Antarctic Bottom Water is not separated by a discontinuity layer from the Warm Deep Water 

 and the position of the boundary between the two is difficult to estimate. None of the samples 

 examined here was collected in this water mass. 



2. Distribution of Species 

 Only the distribution of the species described in the Systematic Account is discussed in this section. 

 This excludes a very few species inadequately described or known only from a few records. Taxo- 

 nomic sequence has been retained only where this is of zoogeographical significance. The species are 

 arranged in order of occurrence from south to north, that is from the ice-edge to the equator. Endemic 

 antarctic polychaetes are considered first, then the cosmopolitan forms and finally the sub-tropical 

 and tropical species. 



Previous work on pelagic polychaetes in the South Atlantic Ocean has been mainly confined to 

 material from particular zones, except for the reports by Monro (1930, 1936) on some of the Discovery 

 Collections, and Friedrich (1950 c) on the ' Meteor ' material, both of which covered the whole area. The 

 Deutsche Sudpolar Expedition (Ehlers, 1913, 1917) and the Swedish Antarctic Expedition (Stop- 

 Bowitz, 1 951) made collections in the Antarctic and occasionally elsewhere, but other expeditions 

 referred to in this section worked either in the Antarctic, or in the Sub-Tropical and Tropical Zones. 



The wide area and numerous stations in the South Atlantic, from which I have examined material 

 from the Discovery Collections, are shown in Text-figs. 1-4, pp. 165-7. Tne extensive hydrological 

 work also carried out by the Discovery Investigations is summarized in the previous section of this 

 report ; it has enabled me to indicate, to a certain degree, the effect of variation in the hydrological 

 environment on the distribution of the pelagic polychaetes of this area. 



Rhynchonerella bongraini 

 (Text-figs. 23-6, Tables 14 and 15, Appendices I and II) 

 The endemic antarctic R. bongraini was collected only in the top 500 m. of water, that is in Antarctic 

 Surface Water and in the upper layers of the Warm Deep Water. The specimens varied between 

 4-15 mm. in length and occurred mainly in samples collected by the N 70 V net; on rare occasions 

 it was caught by the N 100 net. 



The occurrence of R. bongraini in the region of the Greenwich Meridian is shown both in Text- 

 figs. 23 and 24 and in Tables 14 and 15. The temperature and salinity characteristics of the top 

 500 m. of water in which it occurs are shown in Text-figs. 15-21. 



In this region R. bongraini is absent from stations immediately south of the Antarctic Con- 

 vergence and its distribution in the Antarctic Surface Water seems to be controlled more by the 

 influence of the Weddell Drift than by the position of the convergence. The existence of a boundary 

 between Bellingshausen Sea Water and Weddell Drift has already been noted (p. 209), and R. bongraini 

 was never collected to the north of this boundary. 



The records of R. bongraini from the South Sandwich Survey have been plotted in Text-fig. 25 and 

 listed in Appendix II, Table b. Nets were not fished below 250 m., so that only the Antarctic Surface 

 Water was sampled. All the South Sandwich stations lie well within the Weddell Drift (Deacon, 

 1937) so that it is not surprising to find R. bongraini at thirty-two out of the fifty-eight stations. 



The distribution of R. bongraini in the South Georgia area is shown in Text-fig. 26, which includes 

 the following records : 



1 . The Alciopid larvae of Hardy and Gunther (1935) : December-January Survey 1926-7, Sts. 124, 

 210-100 m. (1), WS 35, 51 m. (1), WS 36, 250-100 m. (1) and WS 112, 160-50 m. (1). Of these, I 



