THE SOUTHERN SPECIES OF THE 

 GENUS EUPHAUSIA 



By D. DILWYN JOHN, M.sc. 



(Text-figures 1-40) 

 INTRODUCTION 



THIS report is an account of the adult characters and distribution of ten species of 

 Eiiphausia from southern waters, and of the development from the second Calyptopis 

 stage upwards of five of those species. 



The surface waters of the southern oceans are divided from south to north into three 

 well-defined zones of waters of different origins : the Antarctic, sub-Antarctic and sub- 

 tropical Zones. They are separated from one another by sharp boundaries, because, 

 along the line where two meet, the heavier water of one zone does not mix with the 

 lighter water of the other but sinks below the surface. Most of the species of Eiiphausia 

 described here are found only in one or another of these zones. 



The characters of the species, more particularly those of the copulatory organs of 

 the males, show that five of the ten make one group and four another group. I think 

 they show too that, if it be supposed that the genus Euphausia arose in tropical 

 waters, the individuals of each group represent, in the order that they occur from north 

 to south, successive steps towards the colonization of Antarctic waters by the genus 

 along two distinct lines. 



The ten species of Euphausia whose adult characters are described are : 



E. crystallorophias, Holt and Tattersall E. triacantha. Holt and Tattersall 



E. superba, Dana E. longirostiis, Hansen 



E. frigida, Hansen E. spinifera, Sars 



E. vallentini, Stebbing E. hanseni, Zimmer 



E. hicens, Hansen E. similis, Sars 



The first seven species occur only in the Antarctic or sub-Antarctic Zones, except that 

 E. lucens is found too in the coldest water of the subtropical Zone. E. similis is always 

 present in all but the coldest water of the sub-Antarctic Zone and may occur throughout 

 it ; but it has a wider distribution than any of the other nine species : not only is it found 

 like E. lucens in the coldest water of the subtropical Zone as well as in the sub- 

 Antarctic, but it has been recorded from the neighbourhood of the Philippines and from 

 off the south coast of Japan. To describe these eight species would be to describe a 

 geographical unit, for they are the only members of the genus occurring in the Antarctic 

 and sub-Antarctic Zones. E. spinifera from the subtropical Zone and E. hatiseni from 

 tropical waters are included because they are closely allied to E. longirostris and E. 

 triacantha, and together with them form one of the groups mentioned above. 



All the species have been described before, but the descriptions are in scattered 



