36 



PART I. GENERAL ACCOUNT 



along the hind edge of the crests of the keels (Fig. Ы9Е). Finally, in Sibo- 

 glimim tenue and S. hyperboreum the bridle is represented by a rather broad 

 cuticular tract along which runs a single fine dark thread-like thickening 

 (Fig. ПЩ. [See also pp. 361 and 436.] 



The adhesive plaques 



The adhesive plaques are localized thickenings of the cuticle lying on the 



surface of the adhesive papillae in many species. For the most part they are 



round, oval or horseshoe-shaped on the papillae of the front part of the 



trunk and secreted by many cells of the epidermis (Fig. 25), while on the non- 



Fig. 25. Section through an adhesive plaque of the metameric region of the metasoma of Lamelli- 

 sabella zachsi. 



eg - gland cell ; cut - cuticle ; ep - epithelium ; fin - muscle fibre ; mb - basement membrane ; 

 p - plaque; pu - pulvillus. (After Ivanov, 1960a.) 



metameric and postannular parts of the trunk (Fig. 34C) the smaller rod-like 

 plaques are each produced by a single large cell (Fig. 35). The former type 

 often have the appearance of transversely oval scales with a thickened front 

 edge (e.g. in most Thecanephria, Fig. 34Z), and in Birsteinia), but in 

 Lamellisabella (Fig. 34Д B) they have a complex shape and seem to be rather 

 well adapted as catch mechanisms (p. 47). 



The toothed bristles of the girdles 

 Amongst the epidermal formations may also be included the toothed 

 platelets of the girdles so characteristic of the Pogonophora and recalling, 

 as pointed out by Caullery (1914), the uncini of sedentary polychaetes. 

 [Indeed the term "uncini" is applied to these platelets by such authors as 

 Hartman (1961)]. The location of the toothed platelets has been described 



