SIBOGLINUM SILONE 



299 



Fig. KK133. 



Siboglinum silone 

 Spermatophore. 



males. They are cigar-shaped and quite regu- 

 lar in outline. The filament begins with the 

 ribbon-like proximal section shown in the 

 figure (Fig. KK133). 



The tube is at first the colour of straw, 

 then brown; it is lustrous thin-walled elastic 

 segmented and ringed. The anterior part is 

 transparent, with clearly defined segments 

 which have fine constrictions and transverse 

 wrinkles between them. Each segment is 

 five or six times as long as the tube is wide 

 (Fig. LL133y4). The rings appear gradually, 

 first in the hind part of each segment, then 

 over the whole length of the segment. They 

 are brown in colour and very short - no 

 more than a tenth or at the most a fifth of the 

 diameter of the tube. Often the edge of each ring is dense and thick so that 

 the rings appear almost double. Very often, though not invariably, there are 

 numerous irregularities in the development of the rings. The number of 

 rings in one segment may vary from 16 to 40, but is usually within the range 

 18-25. The first and last rings in a segment are usually longer and thicker 

 than the others (Fig. LL1335). 



In the middle part of the tube the segments become irregular and the rings 

 longer and thicker. At first they usually appear double (Fig. LL133£), then 

 they become single (Fig. LL133.F), and they frequently become irregular. 

 At the hind end of the tube the rings become shorter (narrower), irregular 

 and sometimes double (Fig. LL133G) and finally they fade (Fig. LL133//). 



S. silone most closely recalls S. fedotovi. These two species share the 

 following features: a long mesosoma and small protosoma; a pretentacular 

 groove delimiting the hind end of the cephalic lobe ; a bipectinate tentacle ; 

 three girdles, two anterior and one farther back; and the strong development 

 of the anterior group of teeth on the comparatively large toothed platelets. 

 In both species the hindmost girdle is broken both dorsally and ventrally. 

 The tubes of S. silone and S. fedotovi are also very similar, but in the latter 

 species there are less rings per segment. 



The possession of a pretentacular groove is a very important character. 

 Besides S. silone and S. fedotovi this character is shared by S. ekmani, S. 

 pinnulatwn, S. plumosum and S. japonicum. All these species also possess 

 bipectinate tentacles (at least when it is possible to make out the structure), 



