IDENTIFICATION OF THE SPECIES 55 



IDENTIFICATION OF THE SPECIES 

 For descriptions and figures of E. superba and of its eggs and larvae the following authorities may be 

 consulted, those shown in italics contributing both descriptions and figures, the others descriptions 

 only or documented notices of its occurrence. 



Dana (1850) Hansen (1913) Rustad (1930) 



Dana (1852 and 1855) Tattersall (1913) Ruud (1932) 



Sars (1883) Zimmer(i9i4) Rustad {ig24) 



Sars (1885) Hansen (1915) Eraser (1936) 



Hodgson (1902) Coutiere (1917) John (1936) 



Holt and Tattersall (1906) Tattersall (1918) Bargmann (1937) 



Coutiere (1906) Hansen (1921) Barkley (1940) 



Tattersall (1908) Tattersall (1924) Dell (1952) 



Hansen (1908) Illig (1930) Zimmer (1956) 

 Zimmer (1913) 



The principal papers, in which the most comprehensive descriptions and best figures of the krill or 

 its larvae may be found, are those by Sars (1885), Tattersall (1908), Hansen (1908), Hansen (191 3), 

 Ruud (1932), Eraser (1936), John (1936) and Bargmann (1937). 



In practice the older stages of this euphausian are readily recognised in the plankton not only by 

 their great size and distinctive red coloration, but also by the fact that as a general rule they are 

 captured in such large numbers that the sheer reddish mass of them swamps or blankets the rest of 

 the catch. The older stages of the larvae, from the First Furcilia onwards, and the adolescents both 

 show this distinctive coloration and they too, notably the larvae, are generally taken in such immense 

 numbers that they appear as a red cloud in the samples. In general the stages just mentioned can 

 readily be distinguished in fixed samples (i) by the characteristic manner in which the slender 

 abdominal segments, in a low downwardly directed arc, taper gracefully away to the rear, and (2) by 

 the exceptionally long development of the setae of the thoracic limbs, a development conspicuously 

 more pronounced in this than in any other member of the genus. Without having to resort to dissec- 

 tion the adult male can be recognised at once by the large eyes, heavy chitinization, the some- 

 what slender and reduced appearance of the enveloping carapace and powerful development of the 

 expodites of the thoracic limbs. The eyes of the adult female are distinctly smaller than those of the 

 adult male (Bargmann, 1937, PI. i) and when gravid the former, heavily distended with eggs, is 

 always obvious. 



The eggs, Nauplii, Metanauplii and the three Calyptopis stages are also comparatively easy to pick 

 out. In 1930, during the first voyage of R.R.S. 'Discovery 11', Eraser (1936) definitely established 

 the specific identity of the large euphausian eggs he found in the plankton by comparing them 

 with others shed by gravid E. superba females kept in aquaria. He remarks that their relatively great 

 size together with their characteristic milky or porcelain white colour in reflected light renders 

 them, particularly when present in bulk, comparatively easy to detect, even with the naked eye. Their 

 diameter — o-6 mm. when fresh and only slightly less when preserved — greatly exceeds that of the 

 other euphausian eggs with which they might be confused and which are often present in the samples 

 in considerable abundance. The structure of the egg-shell which is thin, delicate, transparent and 

 unsculptured and the fact that the egg mass almost up to the point of hatching completely fills the 

 shell are other useful aids to identification. There is no oil globule or other mechanism of flotation 

 which suggests they may not be buoyant. In the samples I examined I found, as Eraser found, eggs 

 in all stages of development up to one where the fully formed First Nauplius appeared to be almost 



