ZOOPLANKTON 269 



nordmani being present in the 50-0 m. haul. At the next station seawards, WS 980, they were only 

 present in the 50-0 m. haul (one Podon polyphemoides and twenty Evadne nordmani), the 100-50 m. 

 haul and all other hauls on this line of stations being devoid of Cladocera. 



On the Sylvia Hill line only two E. nordmani were taken at the station closest to the coast (WS 989), 

 and although no specimens were taken on the Orange river line, one specimen of E. nordmani was 

 recorded farther south at WS 1043 on the second survey. 



It was very noticeable during sorting how completely the Ostracoda gave way to Cladocera close in 

 to the land on each line of stations. Here it seems that the marine ostracods constitute an essentially 

 oceanic mid-water group, while the Cladocera were confined to the most neritic part of the coastal 

 current. The two groups showed an almost complete absence of overlap in the first survey samples. 



Ostracoda 

 Mr E. J. lies (1953) has published a report on the ostracods in the collection. Nearly all of these 

 occurred at the offshore stations. As with the mysids, variety rather than numerical abundance 

 characterized the group. Three genera were present, and of one of these, Conchoecia, twenty-three 

 species occurred in the samples. 



Four or five species of Conchoecia predominated, but by far the greatest number were contributed 

 by the species Conchoecia elegans Sars. 



C. elegans mainly inhabited the 500-250 m. layer off the edge of the continental shelf on the three 

 main lines of stations, but there are also indications that it shows a vertical migration, similar to that 

 described by Fowler (1909) in the Bay of Biscay, and more than eighty adults were found in the 

 50-0 m. layer at the night station WS 977. 



C. nasotuberculata Miiller, and C. curta Lubbock, both appeared to occupy a depth distribution 

 similar to that of C. elegans, or perhaps at rather shallower levels. C. alata Miiller was found at 

 greater depths, 500 m. or more, while C. symmetrica Miiller was amongst the deepest species of all, 

 possibly even exceeding 1000 m., the greatest depth of the net hauls. 



C. teretivalvata lies occurred in quite large numbers in the shallower layers, i.e. in samples from 

 250-100 m., except at one station, WS 976, where an anomalous haul of twenty-four specimens 

 occurred in the 750-500 m. layer. 



As previously noted the ostracods did not overlap the Cladocera, and indeed at the inshore stations 

 their niche appears to be filled by the latter group. 



Mysidacea 

 Dr Tattersall (1955) has examined and reported on the collections of mysids, 1 and the following 

 remarks are abstracted from her report. 



Only at one station, WS 1002, were large numbers of individuals taken. Here, in the 50-0 m. haul, 

 there were over 450 specimens of the gregarious mysid, Gastrosaccns sanctus (van Beneden). One 

 small juvenile specimen of the same species was taken rather farther seaward at station WS 1000. 

 Both these stations are somewhat farther south than is normally recorded for this species. 



In spite of the paucity of numbers in the net hauls at the other stations, there was a richness of 

 species in which ten genera and sixteen species were recorded. Many of these occur within the known 

 geographical range of the species. Boreomysis rostrata Illig occurred in the deeper 750-500 m. hauls 

 at the offshore stations. Two species, however, show an interesting deviation from their normal range. 

 Dactylamblyops hodgsoni Holt and Tattersall has previously been recorded only from deep waters in 



1 Her report is on a much larger collection which includes those from the Benguela current. 



19-2 



