SIBOGLINUM VARIABILE 241 



S. tenne is one of the smaller species. The length of the anterior section of 

 the body is no more than 0-5 mm and the breadth of the mesosoma 0-1 mm. 

 The front part of the trunk is 0-075 mm broad and the distance separating 

 the first two from the last girdle is 0-5 mm. 



The rings of the unsegmented tube are most characteristic. Towards the 

 hind end of the filmy, transparent front part of the tube, very numerous, 

 soft delicate transverse fibres begin to appear (Fig. 121G). The greater part 

 of the tube is characterized by a somewhat coarser fibrous structure and 

 possesses double, dirty-brown rings, with indistinct edges (Fig. 121//). In 

 the hinder part of the tube, the fibres disappear and the double rings come 

 to consist of incompletely commingled, brownish blotches of an opaque 

 dense substance (Fig. 1217). The longest tube reached 85-90 mm, and the 

 diameter near the front of the middle section is с. 0T mm. 



Among the species lacking pinnules, S. tenne is nearest to the Arctic form 

 S. hyperboreum, with which it is linked by the possession of a post-tentacular 

 groove, by the fusion of the keels of the bridle, by the development of three 

 girdles in the metasoma and by the common characters of the tubes. It has 

 also features in common with S. variabile (p. 241) and with S. bogorovi 

 (p. 244). The diagnostic features of S. tenue are the following: the broad 

 cuticular bands of the keels of the bridle (in S. hyperboreum they are much 

 narrower), the rudiments of a glandular belt in the mesosoma, the arrange- 

 ment of the toothed platelets in a single row, their comparatively small size 

 and the rather weak development of their anterior teeth, and, finally, the 

 blotchy double rings in the hind part of the tube. 



Material : 26 broken tubes, some with animals. 



Locality: Pacific Ocean to the east of the North Island of New Zealand. 



Depth: 2072 and 3013 m. 



Substratum: calcareous clay or a silty clay sediment. 



18. Siboglinum variabile Ivanov (Fig. 122) 



Ivanov, 1960c: 5, 27, 160, 172, 174, 175-7, 187, 265, Figs. 87, 122. 



This species was taken in 1958 at a station of R.V. Vityaz* situated near the 

 east coast of the North Island of New Zealand. Only two individuals, a male 

 and a female, were extracted from the rather numerous tubes collected. One 

 of the peculiarities of this species appears to be the considerable variability 

 of the tube, which gives rise to the name S. variabile. 



The anterior section of the body is comparatively short, with a length to 

 breadth ratio of 5 or 6 : 1. The short protosoma is sharply divided from the 



