18 



25 Members of the infraorder Physosomata are usually few in number or are 

 rare crustaceans inhabiting mostly the deeper parts of the ocean. Their 

 distribution is governed by regularities common to deepwater pelagic 

 forms. 



The Physocephalata inhabit the surface layers or the middle depths of 

 the ocean; sometimes they are numerous or even highly populous species. 

 Among them, Platysceloidea, near-surface, warm-water animals, are the 

 most characteristic members of the tropical epipelagic ocean fauna. The 

 Vibilioidea and Phronimoidea include species from middle-deep waters. 

 These superfamilies comprise several members that are highly numerous 

 in moderately cold and cold oceanic regions. 



Hence, in order to clearly describe the characteristics of geographic 

 and vertical distribution of hyperiideans, we shall consider the infraorder 

 Physosomata and the principal superfamilies of the Physocephalata 

 separately. 



Infraorder Physosomata 



The deepwater hyperiidean Physosomata fauna of the world ocean has 

 been poorly studied. Even in the most comprehensively investigated 

 Kuril-Kamchatka region of the Pacific Ocean where far more deepwater 

 catches have been made than in any other part of the ocean, the hyper- 

 iidean fauna of the abyssopelagic zone — depths over 3,000 m — is far 

 from fully represented in collections. As for other regions, we cannot 

 say that collections of bathypealagic and abyssal species are complete. 

 This situation compels us, firstly, to refrain from attempting detailed 

 characterization of the area of distribution of hyperiideans of this group, 

 and to confine ourselves merely to a comparison of fauna of all the 

 oceans or their principal climatic zones. Secondly, it must be borne in 

 mind that the faunistic differences observed are largely due to inadequate 

 and nonuniform study of the Physosomata fauna in different oceans and 

 oceanic regions. 



As mentioned earlier, the majority of Physosomata species are rare 

 organisms. This observation pertains mainly to deepwater species inhab- 

 iting the abyssopelagic zone. The population density of bathypelagic 

 hyperiideans is higher and many of them are known from tens of spec- 

 imens. However, the bulk of the Physosomata in collections comprises 

 several species which are found in many catches made at depths. Two 

 of them — Scina borealis and Lanceola clausi — are numerically dominant 

 over the remaining Physosomata in almost every ocean; the others are 

 dominant in limited regions. Thus, besides L. clausi and S. borealis in the 

 Kuril-Kamchatka region of the Pacific Ocean, S. rattrayi keilhacki and 

 L. serrata rank in numbers; in the Antarctic, S. antarctica and L. loveni 

 antarctica; and in tropical regions of all the oceans, S. crassicornis. 



