PENEIDES. 



Sergestidae. 



This family contains the genera Sergestes, Leucifer, 

 Aphareocaris and Petalidum, of which the two last-named 

 are not represented in the "Michael Sars" collections. 



For information regarding the species not treated of 

 in this paper, readers are, above all, referred to Hansen's 

 papers (1896 and 1903). 



Leucifer Reynaudii, H. Milne Edwards. 



This tiny transparent animal, which looks so little 

 like a shrimp, seems to belong exclusively to the surface 

 of the sea. It was taken in the S. E. portion of the 

 area only. 



I have not had access to Milne Edwards' original de- 

 scription; but have determined the specimens by means 

 of Bates' drawings and description in the "Challenger" 

 Report- 



Table of catches. 



St. 



Gear 



m. w. 



Number 



Sex 



29 



1 sn 







1 



Id" 



45 



1 sn 



200 



1 



Id" 



_ 



1 sn 



100 



9 



4? 5d* 



46 



1 sn 







2 



1 ¥ Is" 



47 



Va sn 



40 



13 



8 ? 5d" 



48 



V2 sn 



7800 



1 



Id" 



49 



y 



370 



1 



1 ¥ 



51 



1 sn 







113 



43 ¥ 70 d" 



52 



1 sn 







43 



22 ¥ 21 d* 



8 



9 





184 



105 d" 79 ¥ 



Sergestes. 



For the synonymy of this genus I refer to Hansen (1896). 



Ever since the first Sergestes was captured the genus 

 has been a source of difficulty, and even now, I believe, 

 there is still much to be added to our knowledge of it, 

 especially concerning the role which Sergestes plays as 

 a component of the oceanic plankton. Two circumstances 

 seem to have obscured our knowledge regarding Ser- 

 gestes, (and this applies also to many other oceanic ani- 

 mals), viz: (1) the adults live generally at some distance 

 from the surface and are consequently more difficult to 

 obtain than the small larva;, usually found in the upper- 

 most waterlayers; (2) the adults seem to be powerful 



swimmers and hence were not so easily captured before 

 the introduction of steamships in marine investigations 

 allowed of the deep-sea appliances being towed at a 

 greater speed than was formerly practicable. 



During the "Michael Sars" Expedition in 1910 the 

 Atlantic watermasses were investigated by means of effec- 

 tive tow-nets, etc., and the captures of presumably swiftly 

 swimming animals like fish and prawns were considerable, 

 not to be compared to anything brought home by former 

 expeditions. Our knowledge of the genus Sergestes has 

 been much extended by an examination of the rich 

 material collected. 



Firstly I should like to point out that Sergestes and 

 some other prawns (Hoplophorida; and Pasiphaidee) form 

 an essential part of the oceanic mesoplankton, and pro- 

 bably play an important role as food for fishes, whales 

 and other large aquatic animals. 



Not only are the "Michael Sars" plankton samples rich 

 in quantity, but they also contain many new forms, and 

 have led to a better understanding of the relationship of 

 the forms previously described. Thus of Sergestes four 

 new species are described in this paper, viz: 5. grandis, 

 S. splendens, S. tropicus and S. pectinalus and the adults 

 of two species formerly known only as larva; were found 

 in great numbers in the Atlantic, viz.: 5". armatus, Kr. 

 and 5". corniculum, Kr. 



Since Hansen's two important papers on Sergestes 

 were published (1896 and 1903) our knowledge of the 

 genus cannot be said to have been greately extended. 

 Explorations in the Mediterranean have proved the exi- 

 stence in that sea of a good number of the Atlantic forms 

 (Pesta 1913, u, f). 



The following key is in its main features similar to 

 that given by Hansen in 1896, though synonyms and 

 names applying only to larva; are not included, while 

 some slight alterations are introduced. 5. corniculum Kr, 

 is transferred to group B II, as made necessary by a study 

 of the adult. The same is done with 5. rubroguttatus 

 Wood Mason which undoubtedly is nearly related to it. 



A number of species not captured by the expedition, 

 and of which our knowledge is rather incomplete, are not 

 included, e. g. S. hamifer Wood Mason, etc. 



The species taken by the "Michael Sars" are printed 

 in heavy type and the letters after each name denote the 

 main facts about their distribution, A signifying the At- 

 lantic Ocean, P the Pacific, / the Indian and N the Nor- 

 wegian Sea, M the Mediterranean. 



