362 



of the maxillipeds a row of strong setae occurs, which are much longer 

 in the middle, becoming shorter towards the ends; there are no setae on 

 the outer margin of the outer lobes of the maxillipeds. 



The 6th segment of pereopods I is shorter than the 5th, its posterior 

 margin finely denticulate and without submarginal setae; the claw is 

 finely denticulate in the proximal part of the inner margin, pereopods ill 

 and IV are identical in structure; the short 4th segment broadens distally 

 and the oval 5th segment is 1.5-2 times longer than it; the 5th segment 

 bears long strong setae along the inner margin; the slightly curved 6th 

 segment is barely longer than or equal to the 5th segment; the claw is 

 long, slightly curved, and smooth. 



Unlike in P. abyssorum, of the last three pairs of pereopods, pair V 

 is the shortest and pair VI the longest; the difference in total length of 

 these pereopods depends mainly on the length of the 6th segment, which 

 is 1 .5 times longer than the 5th in pair V and two times longer in pair VI; 

 the posterior distal angle of the 5th segment in pereopods VI and VII 

 bears one long strong seta; the claws of pereopods V-VI or V-VII are 

 2/1 1-2/9 the length of the 6th segment and bear a small fascicle of short 

 setae in the proximal part of the anterior margin. The triangular-oval 

 telson is 2/5-1/2 the length of the basipodite of uropods III. 



Distribution: This is an abundant species in the Sea of Japan and the 

 Sea of Okhotsk. How far it penetrates into the ocean is not known as most 

 researchers have not separated it from the very closely related species, 

 296 P. pacifica (discussed below), which lives in the subarctic waters of the 

 Pacific Ocean. There are references to its detection in the ocean in the 

 coastal areas of northern Japan and the South Kuril Islands. The young 

 of P. japonica live mainly in the upper 50 m layer but adults are found 

 at greater depths as well — right up to 500 m and, in the Sea of Japan, 

 even deeper than 1,000 m, up to the near-benthic layer (~ 3, 000 m). In 

 the Sea of Japan crustaceans larger than 5 mm perform intensive diurnal 

 migrations with an amplitude of about 400 m (Semenova, 1974). 



3. Parathemisto (Parathemisto) pacifica Stebbing, 1888 (Fig. 152) 



Stebbing, 1888: 1420; Bovallius, 1889: 263; Bowman, 1960: 

 345. — oblivia Holmes, 1904: 233. — abyssorum (non Boeck, 1870); Shoe- 

 maker, 1930: 132 (Themisto part.); Thorsteinson, 1941: 90. — japonica 

 Vinogradov, 1956: 211 (part.). 



Length of sexually mature females 4.5-8.5 mm; males somewhat 

 smaller. 



P. pacifica differs from P. japonica in much smaller size of sexually 

 mature individuals and antennae II in females do not exceed antennae I 

 in length as they are somewhat shorter than the head and two subsequent 

 somites of the pereon. Moreover, the pereopods of P. pacifica are armed 

 with much weaker and sparser setae than in P. japonica. 



