14 



PART I. GENERAL ACCOUNT 



— Ct 



that the bridle permits the animal to cling on to the inner 

 surface of the tube as it moves up and down, or serves for 

 temporary anchoring of the front end of the body deep 

 inside the tube. In the larger species the bridle, as a rule, 

 is better developed; it is especially powerfully de- 

 veloped in Lamellisabella johanssoni. 



The region of the mesosoma situated in front of the 

 bridle sometimes appears ringed, in consequence of one 

 (mHeptabrachia gracilis), or two or three (in Я. berin- 

 gensis and Polybrachia — Fig. 7) secondary annular grooves 

 (Ivanov, 1952, 1957a). A pair of auricular lobes are de- 

 veloped in this region in Galathealinum, enveloping the 

 sides of the body (Kirkegaard, 1956a). 



Behind the bridle in some species of Siboglinum [and 

 Nereilinum] there is an epidermal glandular girdle 

 or belt interrupted dorsally and sometimes ventrally 

 {Siboglinum weberi, S. cinctutum, S. fedotovi — Fig. 6, 

 S. plumosum, etc). In S. taeniaphorum and S. atlanticum 

 this girdle is prolonged into a pair of cutaneous glandular 

 ribbon-like tracts, extending along the ventral side 

 of the mesosoma almost to its hind end (Fig. 1285). 

 Sometimes numerous rounded sacculate glands may 

 be seen through the body wall in the mesosomal region 

 (S. pellucidum, Fig. 119^4; Nereilinum murmanicum, 

 Fig. A95C; Siboglino'ides dibrachia, Fig. Y\ZZA\ 

 Lamellisabella zachsi, etc). 



The metasoma or trunk is distinguished by its 

 unusual length and makes up the greater part of the 

 body. It is always divided from the mesosoma by a 

 sharp annular groove, straight or somewhat oblique, or 

 more or less indented on the dorsal or ventral side. In 

 Lamellisabella it is clearly marked only on the dorsal side. 



Fig. 7. Front part of the body of a female Polybrachia annulata from the 

 ventral side. 



b - secondary annuli of the mesosoma ; ct - tentacular crown ; /- bridle ; 

 ms -mesosoma; mts- metasoma; pa - papillae; ps - protosoma ; sv - 

 ventral sulcus. (After Ivanov, 1960a.) 



