ECOLOGICAL GROUPING OF SPECIES 



285 



Group IV 



Oceanic Chaetocerids of medium size. Greatest relative importance 

 from peak of main increase through summer and autumn. Probably 

 most abundant at period of maximum, and in regions subject to neritic 

 influence. Considerable variation in relative importance with latitude 

 on the part of individual members but time distribution very char- 

 acteristic. 



Group III 



Thalassiosira spp. Neritic and ice-edge forms, the majority almost certainly meroplank- 



Asteromphalus parvidus tonic. Relative importance greatest from beginning to peak of main 



Biddulphia striata increase, which is also period of greatest abundance. Decline more 



Eucampia balaustium rapidly than other groups after main increase. Almost absent from 



Chaetoceros flexuosum oceanic waters at other seasons. Autumnal increase seen in few spp. 



Ch. neglectum but only in truly neritic areas. 



Ch. sociale 

 Ch. tortissimum 

 Fragilaria spp. etc. 

 Nitzschia closterium 



Chaetoceros atlanticum 

 Ch. castracanei 

 Ch. chunii 

 Ch. curvatum 

 Ch. dichaeta type 

 Ch. dichaeta tenuicornis 

 phase 



Ch. pendulum 

 Ch. radiculum 

 Ch. schimperianum 



Coscinodiscus spp. (oceanic) 

 Actinocyclus s^fiip. (oceanic) 

 Asteromphalus spp. (other 

 than A. parvulus) 



Other categories of microplankton were considered in the quahtative counts but were 

 quite unimportant except in winter. Dinoflagellates were counted but not tabulated, 

 since they were of no numerical importance at a vast majority of the stations studied. 

 Phaeocystis briicei, the only Antarctic phytoplankton organism that seems important 

 apart from diatoms, could not be counted and must be considered separately. The 

 holozoic constituents of the net hauls have been tabulated as shown below. As one 

 would expect, they form a negligible proportion of the catches except in winter, when 

 the phytoplankton is so very scanty. 



Group V 

 Oceanic Discoidae, mostly small. Of considerable importance in the 

 scanty winter phytoplankton. Almost negligible at other seasons, but 

 doubtless more abundant during main increase. 



HoLozoic Protozoa 



Foraminifera 

 Cymatocyclis spp. 

 Other Tintinnidae 

 Acanthometridae 

 Challengeridae 

 Other Radiolaria 

 Sticholonche 



Metazoa 



Copepoda 



Nauplii 



Other Crustacea 



Limacina juv. 



Ova 



