HEPTABRACHIA GRACILIS 



341 



Ш- 



spermatophores look like tiny flat narrow leaves, 0-2 mm long, gradually 

 tapering towards one end and rounded at the other, filamentary end (Fig. 

 136Я). The thread-like sperm are crowded parallel to each other along the 

 length of the spermatophore. 



A considerable length of the front 

 part of the tube is transparent, with 

 delicate thin limp walls. The greater 

 part of the tube, however, is muddy 

 brown, rather rigid and ringed. A 

 characteristic of the tube is the very 

 uneven length even of adjacent rings, 

 so that an exceedingly short one may 

 lie cheek by jowl with a very long ring 

 (Fig. 137 A). Short clear intervals sep- 

 arate the rings in this part. Towards 

 the hind end of the tube, however, the 

 intervals become longer, and the rings, 

 which are here no longer than the dia- 

 meter of the tube, become much paler 

 in colour and their edges uneven (Fig. 

 1375). The hindmost part of the tube 

 lacks rings altogether and the walls are 

 here white and parchment-like (Fig. 

 137C). One of the longest scraps of 

 tube measured 18 cm long, with a 

 diameter of 0-25 mm near the front 



-.'i--^ 



v 



?,'■■ ■ 



Fig. 137. Heptabrachia gracilis: Tube: A - 

 middle part; В - hind part of ringed region; 

 С - hindmost membranous section. (After 

 Ivanov, 1957л.) 



end and 0-19 mm near the hind end. 



A comparison of the lengths of the 



different sections of the tube, however, 



suggests that the overall length cannot 



be less than 25 cm. The anterior 



transparent section reaches 5-6 cm in length, and the hind parchment-like 



section is at least as long, if not longer. 



H. gracilis is distinguished by a number of features from other species of 

 the same genus. The most important of these are the following: the posses- 

 sion of a single secondary annular groove cutting off the very front part of 

 the mesosoma; the uniserial papillae of the zone of thickening; and the com- 

 paratively large number (3-5) of papillae in each of the transverse metameric 

 rows of the postannular region. In addition, as may be seen from Table 3, 



