SIBOGLINOIDES 325 



on the tentacle and the comparatively narrow glandular ribbons of the 

 mesosoma. 



Locality not known exactly: within 10-mile radius of 48°30'N., 10°0'W. 

 Depth 1100-1250 m.— E.C.S.] 



[2. Genus Siboglinoides Ivanov, 1961 



Ivanov, 1961a: 388, 394-5; Ivanov, 1961b: 138. 



The genus consists of Siboglinidae with two tentacles. The coelom of the 

 mesosoma is occupied by flask-shaped glands both in front of and behind the 

 bridle. There are four or five girdles of toothed platelets in two groups, an 

 anterior and a posterior. There are metameric adhesive papillae on the 

 anterior part of the preannular region. There are no cuticular plaques. The 

 postannular region possesses ventral papillae and dorsal glandular shields. 

 The tube is segmented, with three rings per segment. 



Type of the genus : Siboglinoides dibrachia Ivanov.] 



The only species so far described is the type species, but a second one has 

 been studied and its description is in the press. 



[1. Siboglinoides dibrachia Ivanov (Figs. X-Z133) 

 Ivanov, 1961a: 388-393, Figs. 4-6; Ivanov, 1961b: 138, Fig. B. 



The following description is based on that of Ivanov (1961a), by kind 

 permission of the Editors of Cahiers de Biologie marine. 



In many parts of the Indian Ocean one comes across small fine segmented 

 tubes which regularly have three rings per segment. During 1959 and 1960 I 

 have been able to collect some of these tubes while working on board R.V. 

 Vityaz' on her 31st cruise, in the Timor Sea, south of Java and the Arabian 

 Sea. Unfortunately we only found six tubes, one of which was empty. The 

 animals extracted from the tubes possessed two tentacles (Fig. X133). 



The body of Siboglinoides dibrachia is very fine : the diameter of the meso- 

 soma is no more than 125/x. The fore-part of the body is very short, only four 

 to five times as long as broad. It is at its widest in the region of the bridle 

 which lies just about the middle of the fore-part (Fig. У133Л, В, C). The 

 protosoma is separated from the mesosoma by an unusually distinct groove 

 which dips sharply backwards in the mid-ventral line. The cephalic lobe, 

 which is separated from the protosoma, is heart-shaped or triangular, rather 

 short, rounded at its tip and noticeably broader than the protosoma. With 

 the protosoma it accounts for a quarter of the fore-part of the body. By 

 transparency one can clearly make out the structure of the epidermis of the 



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