200 PART II. SYSTEMATIC ACCOUNT 



Material: one female and one empty tube. 



Locality : the Sea of Okhotsk, to the east of the coast of Sakhalin Island 

 (52°N 144°30'E). 

 Depth: 119-342 m. 



6. Siboglinum japonicum Ivanov (Fig. 105) 



Ivanov, 1960c: 5, 94, 96, 126, 142-5, 158, 196, 264, Figs. 87, 105. 



To all appearances this species forms a characteristic element of the abyssal 

 fauna near the east coast of Japan. A few tubes of S. japonicum were taken 

 amongst many of Diplobrachia japonic a (p. 370) on a cruise of R.V. Vityaz* 

 in the spring of 1957, and three of the tubes contained animals. 



The long fore-part of the body is cylindrical or slightly flattened dorso- 

 ventrally (Fig. \05A, B). In one specimen its length was eight times its 

 breadth, while in another, preserved in a strongly contracted condition, the 

 ration was 6:1. The keels lie in the middle of the fore-part and the front 

 of the mesosoma is marked by a groove which curves strongly back on the 

 dorsal side and almost reaches the dorsal ends of the keels of the bridle 

 (Fig. 1055). The protosoma is long and the cephalic lobe large, short and 

 conical, and in one individual a transverse, pretentacular groove was noticed 

 on the dorsal side (Fig. 105B). In all three individuals the stout but long 

 tentacle was strongly contracted and to a considerable extent covered in 

 abundant transverse wrinkles. The tentacle is attached in the mid-ventral 

 line, just about at or a little in front of the middle of the protosoma (Fig. 

 105^4) and pinnules are absent from its basal part. More distally, there are 

 two closely adjacent, alternating rows of slender pinnules, each c. 0-1 mm 

 long (Fig. 105C). The very delicate, brownish keels of the bridle are fused 

 ventrally but wide apart dorsally, and the ridges of the bridle are weakly 

 developed. In front of the bridle is a weak median ventral furrow, while 

 behind the bridle may be made out a weakly developed brownish glandular 

 belt, which is interrupted on the dorsal side. The boundary between the 

 mesosoma and the metasoma takes the form of a simple annular groove 

 Fig. 105Л, B). 



Fig. 105. Siboglinum japonicum: A - front end of a female in ventral view; В - the same part of 

 another individual from the dorsal side; С - part of the tentacle; D - spermatophore; E - anterior 

 filmy part of tube ; F - anterior part of tube ; G - middle part of tube. 



c- cephalic lobe; «'-lateral part of glandular girdle; /-keel of the bridle; mi -mesosoma; 

 mts - metasoma ; pa- papillae ; pi- pinnules ; ps- protosoma; ^-groove between protosoma and 

 mesosoma ; s 2 - groove between mesosoma and metasoma ; s 3 - groove between cephalic lobe and 

 protosoma ; sv - ventral sulcus ; t - tentacle. 



