34 



confined to waters of the epi- and mesopelagic, its geographic distribu- 

 tion is governed far more by climatic zones than has been observed for 

 35 the deepwater Physosomata. Nearly 50% of the species and over 50% 

 of the genera are from warm waters and have circumoceanic distribu- 

 tion; some rare species with a local area of distribution have been found 

 only in tropical regions. The cold-water regions play a lesser role: they 

 account for 16% of the genera and 30% of the species. Species with 

 panoceanic distribution account for. 10% (6 species). It must be spe- 

 cially mentioned that among the Hyperiidae, the bipolar species {Hype- 

 ria galba, H. medusarum, H. spinigera, Parathemisto gaudichaudi) play 

 a great role; they contribute nearly 10% to the number of species of this 

 family. 



If we compare the faunal abundance of the Phronimoidea of different 

 oceans (Table 9), it will be seen that in the Atlantic and Pacific oceans, 

 it is almost identical. From the Pacific Ocean, 47 species (80% of the 

 world fauna) have been reported, while 45 species are recorded from the 

 Atlantic Ocean; only in the Atlantic Ocean do we come across such gen- 

 era as Bougisia. Undoubtedly, these differences are partly explained by 

 the inadequate study of the group. To a great extent, the same reason can 

 be advanced for the great faunal paucity of the Indian Ocean — 80% of 

 the known genera and 50% of the species. Actually, in the Indian Ocean 

 primarily those species are absent which are known from the tropical 

 regions of the Pacific and Atlantic oceans through reports of single spec- 

 imens; moreover, comparatively fewer species from the known genera 

 have been subjected to comprehensive investigation and revision from 

 the Atlantic or Pacific material, entailing description of new species (gen- 

 era Lestrigonus, Hyperietta, etc.). On the other hand, in the Indian Ocean, 

 northern cold-water species are absent, which play a substantial role in 

 the fauna of the Pacific and Atlantic oceans, and constitute 10% of the 

 fauna of this group (genera Hyperoche, Parathemisto, etc.) (Table 8). 



The superfamily Platysceloidea includes eight families represented 

 by 63 species. All of them inhabit surface waters to a depth of 150-200 m 

 and only some of them go deeper than 200 m (about 10 species); deeper 

 than 500 m, only isolated occurrences have been reported of species from 

 the families Platyscelidae (Platyscelus armatus, P. ovoides), Oxycephal- 

 idae (Streetsia challengeri, Rhabdosoma brevicaudatum), and Pronoidae 

 (Eupronoe armata, E. minuta). 



Special studies conducted in recent years on the vertical distri- 

 bution of the Platysceloidea by methods of layerwise and horizontal 

 catches using large closing plankton nets (Thurston, 1976b; Repelin, 

 1978; and others), have confirmed earlier data. In waters deeper than 

 500 m, only isolated individuals were found, belonging to Lycaea pulex, 



