19 



S. tullbergi and, sometimes, L. sayana. However, in terms of population, 

 none of these species outnumbers the first two mentioned above. 



Vertical Distribution 



Most of the Physosomata were caught in large nets during hauls from 

 great depths to the surface; hence it is not possible to rationally assess 

 their vertical range of habitat. Relatively reliable data are available only 

 for the Kuril-Kamchatka region of the Pacific Ocean. Here, over a vast 

 water body with uniform hydrological conditions during a span of sev- 

 eral years — mainly during the 14th (1953) and 39th (1966) voyages of 

 the "vityaz", at all depths from the surface to 9,000 m, tens of layerwise 

 26 catches were undertaken using BR nets with 1.0 m^ and 0.5 m^ open- 

 ings' and graded catches by horizontal ring-trawl tows with an opening 

 of 2.0 m^ (Vinogradov, 1957, 1970). 



Detailed investigations of the vertical distribution of hyperiideans 

 were also carried out in the region of the Canary Islands during the 

 "SOND" expedition in 1965 (Thurston, 1976b). For plankton collection, 

 two nets with an opening of 1.0 m- were used. Catches were made in 

 many horizontal layers to a depth of 960 m, but regrettably depths for a 

 large part of the bathypelagic and abyssopelagic remained unrepresented 

 in these investigations. 



In examining the nature of the change in Physosomata fauna 

 with depth, we had to rely primarily on the results obtained in the 

 Kuril- Kamchatka region (Pacific Ocean) and in the Canary Islands 

 region (Atlantic Ocean), and use material from different regions as a 

 supplement. 



Based on depth of habitat, the following groups can be identified 

 among the Physosomata: 



1. Epi- and mesopelagic species found from the surface to a depth 

 of 200-500 (750) m. They are found only in warm- water tropical regions 

 of the oceans and are absent in cold-water regions, where waters of the 

 thermosphere are absent. These species include: Lanceola felina, Scina 

 marginata, S. stenopus, S. tullbergi, S. similis, Acanthoscina acanthodes, 

 and sexually mature spawning females of all Mimonectes. 



2. Species primarily inhabiting intermediate waters, from 100-200 

 to 750-1,000 m, and rarely going deeper, beyond 2,000 m. In the 

 Kuril-Kamchatka region, these are Archaeoscina steenstrupi, Chuneola 

 paradoxa, Scina curilensis, S. incerta, S. stebbingi, and possibly, 

 S. submarginata. For the tropical region, besides the foregoing species 

 may be added: S. crassicornis, S. damasi, S. similis, S. nana, S. excisa, 

 S. lepisma, S. vosseleri, S. inermis, and S. rattrayi. 



T Changed from "I.S m"' in Russian text by authors. — ^Ed. 



