SIBOGLINUM BOGOROVI 247 



The tube is most characteristic. In the limp walls of the very long, soft 

 transparent filmy front part are numerous obvious fine transverse wavy 

 fibres (Fig. 1237). This part of the tube then runs more or less gradually 

 into the ringed portion, in which, characteristically, the rings form three 

 separate zones. For most of the length of the tube the rings are as long as the 

 tube is wide, or just a little less. In the first zone, between the muddy-brown 

 homogeneous rings with uneven edges, are narrow clear interspaces with 

 transverse fibres (Fig. \2ZK). Then, in the succeeding zone, the fibres dis- 

 appear from the interspaces, and each ring becomes sub-divided into three or 

 occasionally two, shorter secondary rings, between which are semi-trans- 

 parent spaces, the whole forming a triplet or doublet (Fig. 123L). In the 

 third zone the division into secondary rings disappears and the rings lose 

 their homogeneity, and come to consist of irregular brownish dense patches 

 with clear spaces between them, so that they here acquire a blotchy appear- 

 ance (Fig. 123/kf). Towards the hind end of the tube the rings gradually 

 grow paler and then rather quickly disappear. The largest fragment of tube 

 reaches 118 mm in length, with a diameter near the front end of 0-2 mm. The 

 front filmy part is not less than 45 mm long; the middle, ringed portion 

 reaches 50-55 mm; the hindmost, ringless, filmy part not less than 25 mm. 

 The whole tube must, therefore, be not less than 150-200 mm long. 



S. bogorovi is distinguished from related species, also lacking pinnules, 

 by the absence of any ventral fusion of the keels of the bridle. The post- 

 tentacular groove is a feature shared with S. hyperboreum y S. temie and 

 S. microcephalum. The characteristic features of S. bogorovi include also the 

 irregular arrangement of the papillae in the zone of thickening, the narrow 

 front ends of the toothed platelets, the dumb-bell shaped dorsal glandular 

 shields of the postannular region, and certain peculiarities of the tube, 

 namely, its fibrous front part and the possession of a zone of blotchy rings. 

 This last feature it shares in common with S. tenue. 



Fig. 123. Siboglinum bogorovi: A - front end of a female in dorsal, and, В - in ventral view; 

 C- metameric part of the preannular region from the ventral side (continuation of the part of the 

 body shown in Fig. B); D - region of thickened papillae in ventral view ; E - region of the girdles 

 from the ventral side; F - the same from the dorsal side; G - part of a girdle; H - toothed platelet 

 from a little to one side; / - part of the postannular region; J - front, filmy part of the tube; 

 AT- an anterior part of the tube; L - middle part of the tube; M - hind part of tube. 

 an - girdles; с - cephalic lobe; ci - glandular girdle; со - dorsal ciliated band; da - anterior teeth; 

 dp — posterior teeth ; /- keel of the bridle ; gt - pyriform glands seen by transparency ; ms - meso- 

 soma ; tnts - metasoma ; p - cuticular plaque ; pa - papillae ; ps - protosoma ; s 1 - groove between the 

 protosoma and the mesosoma (post-tentacular groove); sc - dorsal glandular shield; sv - ventral 

 sulcus; t - tentacle; v - ventral papilla. 



