362 PART II. SYSTEMATIC ACCOUNT 



H. ctenophora is distinguished from H. gracilis and H. celebensis by 

 possessing not one but two secondary mesosomal grooves. 



Material : one complete female and one empty tube. 



Locality : off the Pacific coast of North America, a little to the north of 

 Cape Blanko about 40 nautical miles off the coast of Oregon (43°N, 125°W). 

 Substratum : clayey mud. 



Depth: 1376 m.] 



[8. Heptabrachia canadensis Ivanov (Figs. H144, J144). 

 Ivanov, 1962b: 897-9, Figs. 4, 5. 



A single tube of this species, containing an almost complete animal, was 

 taken in a Sigsby trawl north-west of Queen Charlotte Island, opposite the 

 mouth of Dixon Entrance (off the Pacific coast of Canada) at a depth of 

 2500-2600 m. In some respects the animal was like Heptabrachia gracilis, in 

 others like H. abyssicola, but differed from both in several ways. 



The fore-part of the body is cylindrical. The mesosoma is four and a half 

 times the length of the protosoma including the cephalic lobe (Fig. Н144у4- 

 C). The latter is small and triangular. The crown of tentacles is badly 

 damaged and only the basal part of the tentacles remains. There are appar- 

 ently six to eight tentacles but the precise number and arrangement are not 

 clear. Their length is unknown. 



In front of the bridle the mesosoma is scored by two transverse grooves, 

 as in H. beringensis and H. ctenophora. The anterior groove (Fig. HI 44.4) cuts 

 off the front part of the mesosoma as a separate region which is twice as broad 

 as it is long. This groove almost disappears on the ventral side. The second 

 groove runs immediately in front of the bridle and, unlike the first, is more 

 strongly marked on the ventral side (Fig. H144.4-C). The bridle has rather 

 thick keels which do not meet on the dorsal side but are fused together 

 ventrally. The ventral ends are strongly thickened and blackish (Fig. 

 H144Z)), though the remaining part of the keels is colourless. 



The boundary between the mesosoma and the metasoma is very distinct. 

 The metameric part of the trunk is not large; it is furnished with 17 papillae 

 on one side and 18 on the other. The first pair of papillae, lacking cuticular 

 plaques, is larger than the rest and they appear to represent the male genital 

 papillae (Fig. H 144.4). The rest of the metameric papillae are rounded 

 (Fig. H 144.4) and each bears an oval cuticular plaque with a dark thickened 

 anterior rim (Fig. H144£). The transverse diameter of the plaques is 30-33/x. 



