HEPTABRACHIA ABYSS ICOLA 335 



/. Heptabrachia abyssicola Ivanov (Figs. 134-5) 



Ivanov, 1952: 375-7, 388, Figs. 2-6; Zenkevitch, Birstein and Belyaev, 1954: 68, Fig. 10; 

 Zenkevitch, 1954: 76, 80, Figs. 4, 8; Hartman, 1954: 185; Ivanov, 1954b: 72, 76, Figs. 

 2, 8; Kirkegaard, 1956b: 186, Fig. 4; Abrikosov, 1957: 233; Ivanov, 1957a: 463, 464, 468, 

 469, 491, 493, 496, 497, Fig. 59; Vinogradova, 1958: 112; Dajoz, 1958: 233, 236, 237, Fig. 

 6; Ivanov, 1960a: 1553; Ivanov, 1960c: 5, 16, 20, 22, 37, 93, 199, 200-3, 204, 211, 214, 266, 

 Fig. 87, 134-5. 



The cylindrical fore-part of the body, which has a length to breadth ratio 

 of 5-6 : 1, has a simple groove dividing the protosoma from the mesosoma. 

 The conical cephalic lobe is pointed (Fig. 134Д B). The bases of the seven 

 or eight very long tentacles are arranged horseshoe-wise; the pinnules have 

 not been investigated. The yellow keels of the bridle, lying in front of the 

 middle of the fore-part of the body, do not meet ventrally, where they are 

 perceptibly thicker (Fig. 134^4), and taper towards the dorsal ends. A faint 

 median furrow is sometimes noticeable on the ventral surface of the fore- 

 part of the body, while the hind edge of the mesosoma is curved. 



The comparatively small, rounded, adhesive papillae of the front part of 

 the metasoma number 14-20 pairs, each with a round cuticular plaque 

 (Fig. 134^4). This metameric part makes up a tenth of the whole preannular 

 region of the trunk, and the ventral side of the succeeding, cylindrical, 

 non-metameric part carries numerous disordered adhesive papillae. The 

 dorsal ciliated band is well developed, especially its front portion, which 

 begins immediately at the boundary between the mesosoma and the metasoma 

 (Fig. 1345). The male genital papillae are small. The zone of thickened 

 papillae consists of approximately 20 large conical disordered papillae, 

 occupying the ventral side of the trunk (Fig. 134C). The cuticular plaques 

 in the front metameric part of the trunk are 20/x across and very soft. The 

 front edge of each plaque is thickened into a sort of sickle-shaped rim, the 

 remaining part forming a delicate membrane (Fig. 134D). Similar plaques 

 are found also on the papillae of the non-metameric part of the trunk (Fig. 

 134C), but on those of the zone of thickening the plaques are noticeably 

 bigger. There are two girdles, both widely interrupted ventrally and the 

 first girdle dorsally also (Fig. 134£, F). The yellowish toothed platelets, 

 mostly between 10 and 15ju. long, are uniserial, but occasionally the begin- 

 nings of two rows may be seen (Fig. 134G). The teeth of the front group are 

 very small and the front part of the platelet, which they occupy, is somewhat 

 narrower than the rest, colourless and often distinctly demarcated by a 

 transverse line (Fig. 134//). A single large ventral papilla, with an especially 

 large cuticular plaque, lies behind the second girdle (Fig. 134D). The 



