212 DISCOVERY REPORTS 



one species. Of these genera only Thysanoessa occurs in large numbers ; the others, although they 

 appear regularly enough to show a circumpolar distribution, are rarely represented by more than 

 three or four specimens in one sample. 



Siphonophora. Of the three Siphonophores included in the list the nectophores of Diphyes 

 antarctica and Pyrostephos vanhoffeni are easily identified in the adult stage. The third, Dimophyes 

 arctica was thought, until recently, to be equally straightforward, but Captain Totton (1954, p. 121) 

 has found a new species which has previously been confused with D. arctica. It should be pointed 

 out that the proportion of the new species to D. arctica is only small, only one being present among the 

 twelve specimens presented to Captain Totton for examination, and that this by no means invalidates 

 the conclusion that D. arctica has a circumpolar distribution. 



Anthomedusae. The single Medusan considered, Sibogita borchgrevinki is, as far as can be ascer- 

 tained, the only species of this genus to be taken in the Antarctic. 



Polychaeta. The Tomopteris species have been mentioned above. In addition, Vanadis antarctica 

 is the only species found commonly in the Antarctic surface water. 



Chaetognatha. The three members of this group found in the Antarctic surface water are easily 

 distinguishable by their general appearance. Sagitta gazellae is the only flaccid species; this prevents 

 confusion with Eukrohnia hamata which is firm, more or less opaque, 1 has continuous lateral fins and 

 has almost always a distinct oil globule in the gut (Fraser, 1952, p. 10). Sagitta planctonis is altogether 

 a more rigid and opaque species with a stout tail region. 



Echinodermata. The pelagic Echinoderm larva found consistently in the Antarctic surface water 

 is identified here as Auricularia antarctica but as the specimens have not been examined by a specialist 

 it is not impossible that other species may be included under this heading. 



Ostracoda. The Ostracod Conchoecia hettacra would not at first sight appear to be easily and 

 rapidly identified by the methods applied to the larger forms, and in fact because of its small size it 

 has inevitably to be examined at least under a low-power lens. The shell shape and the arrangement 

 of the shell glands then enable a confident identification to be made. This is not to say that all the 

 members of this species including the young stages in the samples have been examined, but that 

 sufficient specimens have been identified for the purpose of this work. 



Copepoda. On the whole the larger common Antarctic copepods are easy to recognize. Calamus 

 acutus has a characteristic triangular shaped head when seen from the dorsal surface which prevents 

 it from being confused with C. propinquus or C. simillimus. The two latter species of Calanus present 

 certain difficulties. The adult C. propinquus is straightforward as it can be distinguished from C. simil- 

 limus by size alone, but to avoid confusion between C. simillimus and juvenile C. propinquus examination 

 of the fifth thoracic limb is necessary. This causes little delay where only the presence or absence of 

 a species is to be decided, as only a few specimens need be examined, but where a count is being made 

 the delay may be considerable. Again Pareuchaeta antarctica is readily identified when adult but 

 confusion may occur between juvenile P. antarctica and P. biloba ; similarly Euchirella rostromagna 

 and E. latirostris may be confused in the younger stages. Thus these two species, Pareuchaeta biloba 

 and Euchirella latirostris are not included in the list of species under consideration. Of the remaining 

 copepods only Candacia sp. presents any difficulty and as mentioned above this is listed only as 

 a genus. 



Amphipoda. The members of this group included in the above list of species are, with the exception 

 of Vibilia antarctica, readily identified. There was some doubt concerning the correct identification of 

 V. antarctica and it was intended to compare specimens with the type specimen, but unfortunately 



1 Remarks concerning the identification of organisms refer to their appearance after preservation in 10% sea water 

 formalin. 



