30 



of the family Cystisomatidae are not found even in the cold waters of 

 the Southern Ocean. On the other hand, the occurrence range of the 

 genera Vibilioides and Cyllopus is fairly restricted; the former inhabits 

 only the tropical Atlantic, while the latter is found only in the waters of 

 the Southern Ocean. Species with such restricted distribution comprise 

 one-third of the fauna of this group (Table 6). 



The richest Vibilioidea fauna is represented in the Atlantic and 

 Pacific oceans, where respectively 81 and 74% of all the species of 

 the group (Table 6) are found. Somewhat less diverse is the representa- 

 tive fauna of the Indian Ocean, apparently attributable to its lesser study. 

 In the cold waters of the Southern Ocean occur only a small number 

 of species (roughly one-third) of the Vibilioidea which are, in general, 

 warm-water types; all of them, except for two species of the endemic 

 genus Cyllopus and Vibilia antarctica, have a wide panoceanic range. 



The superfamily Phronimoidea (families Hyperiidae, Dairellidae, 

 Phronimidae, Phrosinidae), unlike the Physosomata, which includes 

 mainly meso-, bathy-, and abyssopelagic species, is represented 

 exclusively by epi-and mesopelagic inhabitants, and its members rarely 

 penetrate deeper than 800-1,000 m. 



Most genera and species of the superfamily, such as the Hyperi- 

 etta, lulopis, Lestrigonus, Themistella, Phronimella, Phronima stebhingi, 

 and P. colletti, inhabit only the epipelagic zone at depths of 0-100 and 

 0-200 m. Others, such as the Hyperioides, Phronimopsis, Anchylom- 

 era, and Phrosina inhabit the surface and adjacent waters to a depth 

 of 300-500 m, but a major part of their population is confined to the 

 epipelagic zone. All of them have a range of vertical distribution similar 

 to the Platysceloidea group considered below as well as the characteristic 

 tropical (usually circumtropical) range, including the Platysceloidea. 



However, a whole series of genera and species inhabit surface 

 and intermediate waters, sometimes performing migrations of a fairly 

 high amplitude. In the wide range of depths from the surface layer to 

 800-1,000 m, most representatives of the genera Hyperia, Hyperiella, 

 Hyperoche, Parathemisto, and Primno, as well as some species of 

 the genus Phronima (P. atlantica) are encountered. Some of them 

 34 persistently, or at least at night, concentrate in the upper 100-meter layer, 

 while during the day the bulk of the population descends to 200-400 m 

 and even to 400-800 m. Such migrations are performed by, for example, 

 Primno (Thurston, 1976b) and Parathemisto japonica (Semenova, 1974), 

 whereas in other species, diurnal and nocturnal distribution differs little 

 (for example, Phronima atlantica). 



Among the Phronimoidea, there are almost no species not found in 

 the epipelagic zone (Table 7) although there are some in which the bulk 

 of the population is persistently confined to mesopelagic depths. These 



