HEPTABRACHIA CTENOPHORA 357 



[7. Heptabrachia ctenophora Ivanov (Figs. E144-G144) 

 Ivanov, 1962b: 893-7, Figs. 1-3. 



Two new species of Heptabrachia were collected by Z. A. Filatov in 

 November, 1958, when on board R.V. Vityaz' working in the Pacific Ocean 

 off the coast of Canada and the U.S.A. 



Amongst the washings from clayey mud, brought up from a depth of 

 1376 m at a point a little to the north of Cape Blanko, about 40 miles from the 

 coast of Oregon, two ringed tubes were found. One of them contained a 

 complete animal of the genus Heptabrachia. I have named this species 

 H. ctenophora because of its most remarkable feature — the comb-like 

 structure of the keels of the bridle. 



The fore-part of the body is more or less cylindrical (Fig. Е144.Л, B). The 

 very short protosoma is delimited from the mesosoma by a deep annular 

 groove, which dips backwards on the ventral side as a small median notch 

 (Fig. Е144у4). The small conical cephalic lobe is not cut off from the proto- 

 soma (Fig. El 445). The tentacular crown consists of 17 free tentacles which 

 bear pinnules, some 100/u. long, arranged in four dense longitudinal rows with 

 the pinnules alternating in adjacent rows (Fig. F144/4). The base of the 

 crown forms a horseshoe. 



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

 as in H. beringensis (p. 347), and these are cut across by a mid-ventral furrow. 

 The bridle is well-developed ; its keels are almost colourless and meet neither 

 dorsally nor ventrally. The ventral ends are considerably expanded and 

 their structure is very characteristic. The front edge of each keel is an 

 homogeneous transparent rather thick cuticular tract, with a broad trans- 

 parent cuticular membrane attached behind. The latter is crossed by 

 numerous rod-like darker thickenings, perpendicular to the front edge, 

 whose distal ends push out just a little beyond the hind edge of the keel like 

 a ridge of little hillocks (Fig. F1445). The epidermal ridges of the keels 

 are feebly developed. 



The groove between the mesosoma and the metasoma is sharp and has 

 small but clear mid-ventral and mid-dorsal notches directed forward. The 

 metameric section of the preannular region of the metasoma is short, with 13 

 adhesive papillae on each side of the ventral sulcus (Fig. E144^). The latter 

 is wide and the ventral blood vessel is visible through its integument. The 

 papillae are smallish and rounded; they are elongated ovals in shape or else 

 bean-shaped. Each encloses several rounded pyriform glands. The first four 

 pairs of papillae have no cuticular plaques but the rest bear a single small oval 



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