KRYGIER and WASMER: NEW NORTHEASTERN PACIFIC PELAGIC PENAEID SHRIMP 



size, and its terminal hook (present in mature in- 

 dividuals) and the shape of the bipartate external 

 lobes make identification, even of the juvenile 

 stages (Figure 3g-k), possible. 



The thelycum differs from that seen in other 

 species by the pentagonal shape of the plate on the 

 eighth thoracic sternite and the elevated triangular 

 plate on the sixth sternite (Figure 31). 



We have named B. hurkenroadi after Martin D. 

 Burkenroad, whose work on Crustacea, especially 

 the Penaeidae, is well known. 



GEOGRAPHICAL AND 

 VERTICAL DISTRIBUTION 



Shrimps were examined from mid-water trawl 

 collections taken over much of the North Pacific 

 (Figure 4). Bentheogennema hurkenroadi was 

 found only in collections from the northeastern 

 sectors (lat. 52-34°N and east of long. 142°W) 

 (Wasmer 1972). Pearcy and Forss (1966, 1969) ob- 

 served B. hurkenroadi off the coast of Oregon, as 

 close as 28 km to the northern end of the coast and 

 occurring >92 km off the central and south coast. 

 Wasmer (1972) found the greatest concentration 



in the Transitional Water Mass (Figure 5), with a 

 few individuals occurring in the Pacific Subarctic 

 and eastern North Pacific Central Water Masses. 

 It is assumed to be a transitional species, although 

 as is the case for many shrimps, it is not totally 

 confined to a single physicochemically definited 

 water mass (Wasmer 1972). Since B. hurkenroadi 

 is a deep mesopelagic species and most of the 

 available geographical collections were from 

 shallow depths, the known geographic range will 

 undoubtedly be increased by more systematic deep 

 trawls in the eastern Pacific. 



This species was captured in opening-closing 

 nets from the surface to 1,000-m depth. It ap- 

 parently demonstrates a diel vertical migration. 

 The depth distribution is, with few exceptions, 

 below 500 m during the day and below 100 m at 

 night (Table 1). Neither day nor night distribu- 

 tions are confined to a narrow depth stratum but 

 are diffused in concentration over a broad range. 

 The nocturnal migration into the upper waters 

 appears to entail only a small segment of the 

 population with the main concentration remaining 

 at depth. Those migrating above 500 m included 

 both sexes, though the immature shrimp (<ll-mm 



120* 



I50*E 



120 



60» 



I50»E 



I80» 



I50*W 



120* 



Figure 4.— Cruise tracks of the North Pacific from which shrimp were enumerated, indicating mid-water 

 trawl stations (solid dots). Bentheogennema hurkenroadi n. sp. was collected at stations where dot is 

 encircled. 



743 



