238 PART II. SYSTEMATIC ACCOUNT 



long and с 0-15 mm broad; the preannular section of the trunk is 20-30 mm 

 long, and the postannular section 20-25 mm. 



The spindle-shaped spermatophores are 0-16 mm long, with a maximum 

 breadth of 0-015 mm. The end bearing the filament is a little broader than the 

 opposite pole, and the spermatophore tapers down gradually in this direction, 

 but does not come to a sharp point. The base of the filament is rather narrow 

 and ribbon-like (Fig. 120Я). 



The front part of the unsegmented tube is colourless and transparent 

 except for numerous transverse fibres. The middle part of the tube is fibrous 

 and ringed with brown or mud-coloured, rather regular rings, in length 

 about half to two-thirds the diameter of the tube, while the narrow intervals 

 between them are clear and transparent (Fig. 1207). Farther back the trans- 

 verse fibres disappear and the rings anastomose into very short doublets, 

 sometimes irregular in structure (Fig. 1207). I n tne hindmost part of the 

 tube the rings become simple and regular once more, with a length about two 

 thirds or, rarely, one-half of the diameter of the tube (Fig. 120 AT). The largest 

 fragments of tube are about 20 cm long, and 0T5-0-2 mm in diameter near 

 the front end. 



Though a species of the high arctic seas of the western hemisphere, S. 

 hyperboreum is nevethless most closely related to the more southerly species of 

 the Pacific Ocean, namely S. tenue, S. bogorovi and S. variabile. Besides the 

 absence of pinnules, all these species share the following features in common : 

 the presence of a post-tentacular groove (except in S. variabile), the strong 

 degree of development of the anterior teeth of the platelets of the girdles, and 

 the possession of double or even of triple rings in the tube. In the structure of 

 the bridle S. hyperboreum and S. tenue are very similar. S. hyperboreum may 

 be distinguished from S. variabile by the presence of not two but three 

 girdles, and by the unsegmented tube, and from S. bogorovi by the three 

 girdles and by the ventral fusion of the keels of the bridle. 



Material : some dozens of tubes, some containing animals. 



Locality: the Greenland Sea to the east of Lambert Land (79°N 20° W). 



Depth: 217 m. 



Substratum: brown silt with pebbles. 



17. Siboglinum tenue Ivanov (Fig. 121) 



Ivanov, 1960c: 5, 27, 30, 127, 134, 160, 172-4, 177, 180, 188, 197, 264, Figs. 87, 121. 



In a collection of benthos taken on a cruise of R.V. Vitya£ in 1958 near the 

 east coast of the North Island of New Zealand, amongst tubes of S. variabile 



