174 DISCOVERY REPORTS 



1938; Karcher, 1940) only from the skin-film of whales, in which it had for long been recognised 

 (Nemoto, 1958) as the dominant form, and had not been recorded free in the plankton. In view of 

 these findings Barkley suggests that the Cocconeis cells may get into the water accidentally, it being 

 conceivable that they sometimes get brushed off the whale ' purely mechanically ' through physical 

 contact with the krill. He adds, however, that it might also be supposed that, since the whales from 

 which his samples were taken were infected with Cocconeis, both frustules and spores of this species 

 may occasionally be liberated into the sea. Hustedt (1958) also reports the rare occurrence of 

 C. ceticola in the stomach samples he examined from south of Kerguelen. 



Hustedt (1958) also calls attention to the frequency of occurrence of Fragilariopsis antarctica 'und 

 einige kleine zentrische Diatomeen ', notably Thalassiosira gracilis and Coscinodiscus lentiginosus, in 

 the stomachs, and adds the following long list to Barkley's original findings : 



Diatoms from krill stomachs collected south of Kerguelen, the regularly or more commonly occurring 



species being shown in bold type 



Asterotnphalus hookeri Micropodiscus oliveranus 



Asteromphalus hyalinus Navicula criophila 



Biddiilphia weissflogii Navicula trompii 



Chaetoceros bulbosus Nitzschia harkleyi 



Charcotia actinochilus Nitzschia bicapitata 



Cocconeis gaussi Nitzschia sicula var. rostrata n.var. 



Coscinodiscus lentiginosus Pleurosigma directum 



Coscinodiscus pseudodenticulatus n.spec. Rhabdonema minutum 



Coscinodiscus stellaris var. symbolophorus RhapJioneis amphiceros 



Coscinodiscus tabularis Rhizosolenia styliformis forma longispina 



Coscinodiscus tumidus Thalassiosira antarctica 



Fragilariopsis cylindricus Thalassiosira gracilis 



Fragilariopsis obliquecostata Thalassiothrix antarctica 



Fragilariopsis rhombica Tropidoneis belgicae 



Fragilariopsis ritscheri n.spec. Tropidoneis glacialis 

 Hyalodiscus scoticus 



While the predominance of Fragilariopsis antarctica and the minor degree of dominance of some 

 other small, spineless diatoms in the stomachs seem to point to some measure of selective feeding, 

 the proper interpretation of these findings, as Steuer (1910) and Hart (1942) point out, is rendered 

 exceedingly diflRcult owing to the great differences that exist in the degree of silicification of the 

 frustules of the various diatom species. The majority of the more commonly occurring stomach forms 

 recorded by both Hart and Barkley are strongly silicified, forms that tend to persist in a recognisable 

 condition in faecal pellets, bottom deposits and bird guano, being encountered, for instance, with 

 particular regularity (Chun, 1903; Karsten, 1905; Neaverson, 1934) in the diatomaceous muds and 

 diatom oozes from the shallow and deep-sea floor. It may be, therefore, as Hart remarks, that the 

 more typically oceanic, less strongly silicified, forms are quite as important as food for the krill, but 

 as a rule are digested too rapidly and too thoroughly to be readily identified in the stomachs. Recognis- 

 able fragments of the more poorly silicified oceanic species such as Chaetoceros are rather rare, he 

 states (Hart, 1934), even in the crop, the contents of which in krill from water in which such species 

 are dominant presenting the appearance of a 'green porridge'. In regard to the Chaetocerids he 

 remarks that spine fragments of the large C. criophilim indicate that the adult krill are capable of 

 triturating and swallowing the larger diatom species in addition to possessing a fihering mechanism, 

 while the several references in his notes to pieces of Thalassiothrix and the immensely long 

 Synedra would point it seems to the same conclusion. Hustedt (1958) records C. criophilum fragments 



