326 



PART II. SYSTEMATIC ACCOUNT 



■ pi 



— t 



]—P s 



— mts 



Fig. X133. Siboglinoides 

 dibrachia : Front end of the 

 body from the dorsal sur- 

 face. 



tns - mesosoma ; mts - me- 

 tasoma ; pi - pinnules ; ps - 

 protosoma; t - tentacle. 

 (After Ivanov, 1961a.) 



cephalic lobe and protosoma, which consists of tall 

 cylindrical cells with numerous gland cells filled 

 with clear secretion scattered amongst them 

 (Fig. Y1335). 



The two tentacles are attached to the body side 

 by side and the right tentacle is sometimes perhaps 

 a little thicker than the left (Fig. ХХЪЪА). They are 

 very long and furnished with sparse short pinnules 

 attached in a single longitudinal row (Fig. X133). 

 The basal part of the tentacles lacks pinnules. The 

 tentacular epidermis is rather thick. 



The mesosoma tapers towards its hind end. The 

 part lying in front of the bridle has an epidermis as 

 thick as that of the protosoma; the rest has a thin 

 epidermis. The keels of the bridle are thin and 

 colourless. They are situated on distinct ridges, 

 which taper towards their dorsal ends and become 

 much wider on the ventral surface. The keels are 

 fused ventrally but do not meet dorsally (Fig. 

 У133Л, B, C). 



The strong development of the multicellular 

 flask-shaped glands in the coelom of the mesosoma 

 can be regarded as a most distinctive character of 

 this species. Contrary to those of many other species 

 of Pogonophora, these glands are developed not 

 only in the posterior part of the mesosoma, but also 

 in front of the bridle where they are readily seen by 

 transparency (Fig. Y133, А, В, C). The boundary 

 between the mesosoma and metasoma is marked 

 by a deep groove which is transverse on the dorsal 

 side but curves backwards on the ventral side 

 (Fig. У133Л, В, С). 



The metameric region of the metasoma is two or 

 three times as long as the fore-part of the body 

 (Fig. Y133y4). The ventral sulcus between the meta- 

 meric glandular papillae is plainly marked. The 

 papillae are rounded and lack adhesive plaques. 

 They become larger towards the hind end of the 

 region. Each one contains a single large pyriform 



