268 DISCOVERY REPORTS 



ZOOPLANKTON 



On both of the ' William Scoresby's ' surveys net hauls were made to sample the zooplankton. Full 

 particulars are given in the Station List (1953). On survey I these consisted of a series of vertical hauls 

 with the ' Discovery ' N 70 V net, and were taken only on the three main latitudinal lines of stations. 

 On survey II the hauls were extended to include a surface haul with a metre stramin net (N 100 H) at 

 all stations and in addition an oblique haul with a metre stramin and 70 cm. net (N 100 B, N 70 B) 

 was made at all ' full stations ' — that is, again on the latitudinal lines of stations. 



One of us (T.J.H.) has sorted the zooplankton hauls from survey I, and the material has so far as 

 possible been distributed to specialists in the various groups. Reports on some groups have already 

 been published, and we present a synopsis of the findings of these. Where it has not yet been possible 

 to find specialists to work up the groups, they have been provisionally identified and the results are 

 used in the following general account, sometimes merely to give a picture of the distribution of the 

 group as a whole. Some important groups, notably the Copepoda, have not yet been dealt with. 



The zooplankton samples from survey II have not yet been sorted, apart from some groups — fish 

 eggs and larvae, Cumacea and Chaetognatha — whose distribution had proved unusually interesting 

 during the first survey. These results are included in the following account. 



POLYCHAETA 



Most of the polychaets in the collection were larval or juvenile forms. These have not yet been 

 examined in detail and it is hoped that they will be dealt with separately at a later date. It is interesting 

 to note, however, that some seemed to show a tendency towards a prolonged post-larval sojourn in the 

 plankton over the regions where the bottom waters were exceptionally deficient in oxygen. 



Chaetognatha 

 The chaetognaths in the collection from survey I have been examined and identified by Mr P. M. 

 David, and will be dealt with in a separate report by him. The following notes have been made from 

 the figures kindly supplied by Mr David. 



The distribution of the species seems to follow a rather similar pattern on all three lines of stations. 

 Close to the coast in the surface-layers Sagitta friderici Ritter-Zahony was dominant. Immediately 

 seawards of this, S. serratodentata Krohn became the dominant species, still, however, in the shallower 

 waters of the continental shelf, although this latter species was also found in smaller numbers at the 

 oceanic stations WS 977 and 996. S. decipiens (Fowler) occupied a position just off the edge of the 

 continental shelf and generally somewhat deeper in the water column, the main centre of abundance 

 varying from line to line in depths of about 100-400 m. 



Eakrohnia hamata (Mobius) was concentrated mainly farther seawards than the Sagitta decipiens, 

 in the deeper layers, while above the Enkrohnia hamata population, varying numbers of Sagitta 

 minima (Conant) and S. lyra (Krohn) were taken. Some numbers of S. lyra were also taken at station 

 WS 978. 



Entomostraca 

 Dr J. P. Harding has very kindly confirmed the identification of the specimens of Cladocera which 

 were picked out from the samples. Both Evadne nordmani Loven and Podon polyphemoides Leuck. 

 were present in the collections, and Evadne nordmani was the relatively more abundant species. 



The Cladocera were present only at the stations lying close to the coast. Off Walvis Bay at WS 981, 

 they reached their greatest concentration, more than 600 Podon polyphemoides and nearly 2200 Evadne 



