HEPTABRACHIA CTENOPHORA 



361 



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disappearing. The hind end of the A & 



tube has irregular clear rings out- 

 lined by narrow dark borders (Fig. 

 G144C). The one inhabited tube 

 was 281 mm long, its anterior 

 diameter с 0-7 mm and its pos- 

 terior 0-5 mm. The empty tube 

 was 225 mm long and 0-5 mm in 

 diameter. 



Heptabrachia ctenophora shares 

 many features with H. beringen- 

 sis including: the approximately 

 equal size of the body, the 

 comparatively large number of 

 tentacles (12-13 in H. beringensis 

 and 17 in H. ctenophora), the pos- 

 session of two secondary annular 

 grooves around the mesosoma in front of the bridle, and the small number 

 (10-11) of papillae in the zone of thickening. There are many similarities too 

 in the structure of the tubes. The new species, however, is readily dis- 

 tinguished from H. beringensis by the poorer development of the metameric 

 part of the trunk and especially by the extraordinary structure of the keels of 

 the bridle (compare Fig. F1445 with F144C). 



The strange comb-like structure of the keels of the bridle distinguishes 

 H. ctenophora from the majority of Polybrachiidae. Something similar is 

 found only in the bridle of Diplobrachia, Lamellisabella ivanovi, Siboglinum 

 tenue and S. minutum. In these species, however, transverse cuticular rodlets 

 are attached to the hind edge of the main cuticular band of the bridle (Figs. 

 149£, 152Л, 169^), or they lie across it (Figs. 12Ы-С, 124C). In Hepta- 

 brachia ctenophora, on the other hand, the rodlets are completely enclosed in 

 an homogeneous cuticular membrane. 



Fig. G144. Heptabrachia ctenophora: the tube. 

 A - near the front; В - in the middle; С - near 

 the hind end. (After Ivanov, 1962b.) 



Fig. F144. Heptabrachia ctenophora: A - part of a tentacle; В - the ventral end of a keel of the 

 bridle; С - the same in H. beringensis; D - the zone of thickened papillae from the ventral side; 

 E - cuticular plaques from the metameric region of the metasoma, and F, from the zone of thickened 

 papillae ; G - the region of the girdles from the dorsal and, H, from the ventral side ; / - part of a 

 girdle; J - a toothed platelet from the side; К - part of the postannular region from the ventral 

 side; L - plaques from the postannular region. 

 an - girdles; p - plaques; pa - papillae; pi - pinnules. (After Ivanov, 1962b.) 



