2 6 2 DISCOVERY REPORTS 



amount collected in the higher latitudes to that in the lower to vary between 14: i (Meteor) to 4-5 : 1 

 (Discovery). Only a few species, occurring in large numbers, make up the abundant plankton in the 

 upper 150 m. of water in the Antarctic Zone (Hardy and Gunther, 1935), whereas in the Sub-Tropical 

 and Tropical Zones many species form the small standing crop (Sverdrup, Johnson and Fleming, 

 1946). 



The twenty-nine polychaetes examined in this report conform to this general pattern of plankton 

 distribution. The most abundant is the cosmopolitan Pelagobia longicirrata which occurs in large 

 numbers in the Antarctic Zone. This species is particularly abundant along the Greenwich Meridian 

 in the top 100 m. of water and around South Georgia between 250-50 m. The endemic antarctic 

 Rhynchonerella bongraini is also abundant but being more restricted in its distribution than Pelagobia 

 longicirrata has not been collected so extensively. The nine other species inhabiting the Antarctic 

 Zone do not appear in large numbers ; seven of them are cosmopolitan or widely distributed. Sixteen 

 species appear to be limited in their southerly distribution by the Sub-Tropical Convergence but 

 none of them occurs in abundance. Only the cosmopolitan Tomopteris septentrionalis and T. planktonis 

 have been collected in large numbers in the Sub-Tropical Zone off South Africa in a region where 

 intensive collections were made. 



The following points of interest have emerged from the present survey : 



1. There are no families of pelagic Polychaeta endemic to any hydrological zone in the South 

 Atlantic Ocean. 



2. There are no endemic genera of pelagic Polychaeta in the Antarctic Zone. 



3. The following three species of pelagic Polychaeta are endemic to the Antarctic Zone: 1 

 Rhynchonerella bongraini, Vanadis antarctica, Tomopteris carpenteri. 



Rhynchonerella bongraini was collected only in the top 500 m. of water in the Antarctic Zone within 

 the Weddell Drift, East Wind Drift and the upper layers of the Warm Deep Water. 



Vanadis antarctica probably occurs in all water masses in the Antarctic Zone. It is very similar, 

 morphologically, to V . longissima and with it may represent two geographical races of one 

 species. 



Adult Tomopteris carpenteri were found in all explored water masses of the Antarctic Zone. The 

 smallest specimens of this species, however, were collected only around South Georgia. 



4. In addition to Tomopteris carpenteri, two other species of tomopterids are known from the 

 Antarctic Zone ; T. planktonis and T. septetitrionalis. All three species are very closely related and it is 

 possible that the endemic T. carpenteri has evolved from one of the others (both cosmopolitan) as an 

 isolated antarctic form. None of these species has a first pair of chaetigers, rosette glands, spur glands 

 or a tail. 



5. There are no endemic species of pelagic Polychaeta in the Sub-Antarctic Zone 2 , and no species 

 appears to have its northern limit of distribution at the Sub-Tropical Convergence. 



6. Vanadis longissima is the only species (or geographical race of a species) of pelagic Polychaeta 

 with its southern limit of distribution at the Antarctic Convergence ; it was collected only in the Sub- 

 Antarctic, Sub-Tropical and Tropical Zones. 



7. The genera Krohnia, Alciopa, Naiades and Lopadorhynchus have not been collected south of the 

 Sub-Tropical Convergence ; they may be confined to warmer waters. 



1 Antinoe pelagica Monro, 1930, is known only from two records in the Antarctic Zone; these are insufficient to warrant 

 listing this species as endemic. 



2 Tomopteris kempi was collected only at St. 4 very close to the Sub-Tropical Convergence, either in the Sub-Tropical 

 or Sub-Antarctic Zone. If future collections show it to be confined to the latter it will be the only known endemic Sub- 

 Antarctic pelagic polychaete. 



