4. MUSCULATURE AND PAPILLAE 



47 



In the Thecanephria (except Zenkevitchiana) and in Birsteinia, amongst 

 the Athecanephria, the metameric papillae are each furnished with a cuticular 

 plaque which is always secreted by a group of many epidermal cells. The 

 plaque is situated at the very tip of the papilla, but in Birsteinia, Lamellisa- 

 bella and Spirobrachia they lie on special oval or heart-shaped pulvilli 

 (Fig. 34^4). In the majority of species the plaques look like transversely oval 

 (or, in Heptabrachia abyssicola, round) scales, each with a thickened brown 

 or black front rim. Their dimensions in different species may vary between 

 15 M and 110/x (Fig. 34/)) (Ivanov, 1952, 1957a). 



In Lamellisabella the plaque may take on a rather peculiar shape. As in 

 other Pogonophora, it is scale-like and semi-transparent, and tapers towards 

 the back and side edges. Its outline is circular. The front rim of the plaque is 



^, 



Fig. 34. A - adhesive papilla of Lamellisabella johanssoni from the metameric region of the metasoma ; 

 В - adhesive plaque of the same species in side view; С - papilla of the same species from the non- 

 metameric region of the metasoma ; D - adhesive plaque of Zenkevitchiana longissima from the 

 middle region of the metasoma. 



ap - apodeme of plaque; me - membrane of plaque; p - plaque; pa - papilla; pu - pulvillus. 

 (After Ivanov, 1957a.) 



