SIBOGLINUM SERGEEVI 



319 



its keels do not fuse dorsally, as they do in the latter, but instead merely 

 approach one another. The keels are brown and lie on a narrow ridge, so 

 that, although they are delicate, they are very noticeable. Their ventral 



Fig. XX133. Siboglinum sergeevi: General view. 



an - girdles ; с - cephalic lobe ; со - dorsal ciliated band ; /- bridle ; g - glandular area ; ms - meso- 

 soma; mts - metasoma; pa - papillae; pa 1 - papilla of the zone of thickening; pan - postannular 

 region of the trunk; ps - protosoma; sc - dorsal shield; sv - ventral sulcus; t - tentacle. 



