400 PART II. SYSTEMATIC ACCOUNT 



a little under-developed or even reduced to a mere detached fragment. The 

 transverse plaques of the metameric papillae are с 25/x across. The only 

 known specimen is a male in which the large genital papillae overhang the 

 back edge of the mesosoma and slant towards each other at the front (Fig. 

 1595). Spermatophores have not been found in the sperm ducts. 



The various parts of the body have the following dimensions : length of 

 the tentacles, 20 mm (in a strongly contracted condition) ; length of the fore- 

 part of the body, 4 mm; breadth of the mesosoma, 1-3 mm. 



The tube is unknown. 



The comparatively weakly developed, delicate, slender keels of the bridle, 

 which do not meet ventrally, easily distinguish P. barbata from other species 

 of this genus. In contrast with P. annulata there are only two secondary 

 grooves on the mesosoma. The large number of tentacles is also diagnostic. 



Material : one incomplete specimen. 



Locality : the southwestern part of the Bering Sea. 



Depth: 3792-3802 m. 



3. Polybrachia gorbunovi (Ivanov) (Fig. 160) 



Ushakov, 1940: 77 (as Lamellisabella zachsi)\ Ivanov, 1949: 79-84, Figs. 1, 2 (as 

 Lamellisabella gorbunovi); Ivanov, 1952: 372 (as L. gorbunovi); Zenkevitch, 1954: 77, 

 Fig. 9 (as L. gorbunovi); Zenkevitch, Birstein and Belyaev, 1954: 66, 68, Fig. 10 (as L. 

 gorbunovi); Hartman, 1954: 185 (as L. gorbunovi); Ivanov, 1954b : 69, 79 (as L. gorbunovi); 

 Kirkegaard, 1956a: 79 (as L. gorbunovi); Kirkegaard, 1956b: 186, Fig. 4 (as L. gorbunovi); 

 Ivanov, 1957a: 431, 492, 494, Fig. 59 (as Polybrachia gorbunovi); Vinogradova, 1958: 112 

 (as P. gorbunovi); Dajoz, 1958: 225, 236, 237, Fig. 6 (as Lamellisabella gorbunovi); Ivanov, 

 1960a: 1611 (as Polybrachia gorbunovi); Ivanov, 1960c: 6, 8, 98, 231, 235, 237-8, 239, 266, 

 Figs. 87, 160 (as P. gorbunovi). 



This species was described by Ivanov (1949) from one badly preserved 

 specimen under the name of Lamellisabella gorbunovi. When the material was 

 sectioned, however, the structure of the tentacular crown and other features 

 indicated that it should be ascribed to the genus Polybrachia (Ivanov, 1957a). 

 The cuticular plaques and the tube also lend credence to this ascription, but 

 such characteristic features of Polybrachia as the possession of an external 

 division between the protosoma and the mesosoma, a separate cephalic lobe, 

 and secondary grooves in the front part of the mesosoma, could not be 

 observed because of the bad state of preservation of the material. In the 

 original description of this species (Ivanov, 1949) there were several errors 

 which were later corrected on the basis of the study of the sectioned material 

 (Ivanov, 1957a). 



