SIBOGLINUM PELLUCIDUM 235 



The metameric part of the preannular region of the metasoma is thinner 

 than the fore-part of the body (Fig. 119 A), and the deep ventral sulcus is 

 bordered by regular rows of oval glandular papillae, devoid of chitinoid 

 plaques. The well-developed dorsal ciliated band begins at the front of the 

 metasoma. Two girdles of toothed platelets lie far apart, with as much as 

 3 mm between them. The elongated platelets, tapering slightly towards the 

 front end, are uniserial (Fig. П9С), and their surface is covered with com- 

 paratively large teeth of which the first group occupies about one-third of 

 the total area of each platelet (Fig. 119D). The platelets are 9-12/x long. 

 Nothing is known of the postannular region of the trunk. 



The tentacle is с 10 mm long; the fore-part of the body is 0-9 mm long 

 by 0-14 mm broad, while the front part of the metasoma is only 0-1 mm 

 broad; the preannular region of the trunk in one individual studied was 

 31 mm long and the postannular region с 60 mm. The overall length of the 

 body, including the tentacle, must, therefore, reach about 10 cm. 



The spindle-shaped spermatophores, tapering gradually towards the end 

 without the filament (Fig. 119£), are at least ten times as long as broad, and 

 reach a length of 0-14 mm. 



The first half of the tube is very soft, colourless, glassily transparent and 

 limp. Then very regular transparent colourless rings begin to appear, whose 

 length is half the diameter of the tube. The interspaces between the rings are 

 short and covered with delicate transverse wrinkles (Fig. 119.F). The hind 

 part of the tube is distinguished by slightly denser, but still transparent, 

 pale yellow rings, whose length is only one-third of the diameter of the tube, 

 and which possess a smooth shining lustrous surface. The intervals between 

 these rings take the form of thin, flexible membranes, usually constricted 

 (Fig. 119G). A considerable length of tube at the very end is devoid of rings 

 and as transparent as the front part. The longest fragment of tube reached 

 10 cm in length, of which 6 cm was taken up by the front colourless part. 

 The diameter near the front end is 0-15 mm. 



Amongst the species lacking pinnules S. pellacidum is distinguished by the 

 absence of both post-tentacular groove and glandular girdle in the mesosoma. 

 As in S. bogorovi, there are two girdles of toothed platelets close together. 

 5. pellucidum may be distinguished from S. bogorovi by the fusion of 



bridle ; gt - globular glands of the mesosoma seen by transparency ; ms - mesosoma ; mts - metasoma ; 

 pa - papillae; ps - protosoma; s 1 - groove between the protosoma and the metosoma; s 2 - groove 

 between the mesosoma and the metasoma ; sv - ventral sulcus ; t - tentacle. (А, В, E, F, G after 

 Ivanov, 1957a.) 



