254 PART II. SYSTEMATIC ACCOUNT 



The spermatophores are unknown. 



The front part of the unsegmented tube has transparent, filmy walls, 

 containing transverse fibres (Fig. 126G). The middle part of the tube is free 

 of fibres and ringed with smooth regular transparent almost colourless 

 rings, with even edges (Fig. 126//). For the most part, they are as long as the 

 tube is wide, but occasionally one may encounter longer or shorter rings. In 

 the hind part of the tube, rings predominate which are one and half to two 

 times as long as the diameter of the tube. The transparent interspaces be- 

 tween the rings are small, and the walls of the tube are here covered with 

 transverse wrinkles and lightly constricted between rings. The largest frag- 

 ments of tubes reach 74-78 mm in length and 0-23-0-25 mm in diameter 

 near the front end. 



S. norvegkum somewhat recalls S. pellucidum from the Bering Sea, but it is 

 distinguished from it by the more highly developed, continuous, uninter- 

 rupted keels of the bridle, by the presence of a glandular girdle in the 

 mesosoma, by the many-rowed arrangement of the toothed platelets in the 

 metasomal girdles, by the longer rings of the tube, and by the fibrous 

 structure of the anterior part of the tube. S. norvegkum is related to many 

 species lacking pinnules by the possession of a glandular girdle, but it is 

 distinguished from them by the relatively long protosoma. The chief 

 distinctions from S. hyperboreum lie in the absence of any post-tentacular 

 groove, in the different structure of the bridle, in the weaker development of 

 the front teeth of the platelets, and in the structure of the tube. It may be 

 distinguished from S. inerme by the greater development of the glandular 

 girdle, by the length of the protosoma, by the arrangement and peculiarities 

 of the toothed platelets, and by the structure of the tube. 



Material: 6 tubes, of which 2 contained animals — one male and one female. 



Locality: the Norwegian Sea to the west of the Shetland Isles; at a depth 

 of 120 m, and to the west of the Norwegian coast at a depth of 1165 m. 



22. Siboglinum robustum Ivanov (Fig. 127) 



Ivanov, 1960c: 5, 12, 18, 129, 151, 154, 174, 186-8, 197, 264, Fig. 87, 127. 



One of the most clearly distinguished species of Siboglinum is S. robustum, 

 a single specimen of which was found together with S. buccelliferum and 

 S.frenigerum in a trial dredging made by R.V. Vityaz? in 1957, in the northern 

 part of the Coral Sea. The fore-part of the body is a little flattened dorso- 

 ventrally and comparatively short, with a length to breadth ratio of 4| : 1 

 (Fig. 127^4, B). The bridle lies a little in front of the middle of the anterior 



