202 PART II. SYSTEMATIC ACCOUNT 



The broad dorsal ciliated band begins at the front edge of the metasoma. 

 The 65-70 pairs of metameric papillae of the trunk are large and more or less 

 rounded, and the ventral sulcus between them is narrow (Fig. 105 A). In 

 each papilla may be seen a single pyriform gland. In the hind part of the 

 metameric region the papillae become larger for a stretch and then the region 

 of the trunk possessing small rounded disorderly papillae begins immedi- 

 ately. The genital papillae of the male are not large, but nevertheless meet in 

 the mid-line. The zone of thickened papillae, the girdle region and the post- 

 annular section remain unknown. 



The tentacle is not less than 8 mm long; the fore-part of the body is 

 1-4-1-85 mm long; the breadth of the mesosoma is 0-2-0-25 mm; the length 

 of the metameric part of the preannular region is с 6 mm. 



The spermatophores are shaped like narrow spindles, almost parallel- 

 sided for the greater part of the length, then gradually tapering down to a 

 point at the opposite end from the filament. This latter is very long and 

 slender, but has a thickened base (Fig. 105Z)). The spermatophore is about 

 0-2 mm long, with a greatest breadth of about 0-014 mm in the middle. 



The rings of the unsegmented tube are rather coarse. The front filmy 

 ringless portion is colourless, transparent and limp. Then, in the walls of the 

 tube appear, little by little, numerous transverse fibres (Fig. 105£). The walls 

 gradually become thicker and turn brown, and rings begin to appear. The 

 main part of the tube has well-developed, not very regular, coarse, muddy- 

 brown rings, whose edges are uneven, and in the stouter tubes the rings are 

 very dark brown and coarse. They vary noticeably in length, but are always 

 shorter than the diameter of the tube (Fig. 105.F). The narrow clear inter- 

 spaces between them are transversely wrinkled, and possess coarse, brownish 

 transverse fibres (Fig. 105G). The largest fragment of tube is about 100 mm 

 in length and 0-28-0-32 mm in diameter. 



The arrangement of the pinnules and the development of a pretentacular 

 groove suggests that S. japonicum must be closely related to those species 

 possessing a bipectinate tentacle (S. ekmani, S. pinnulatum, S. fedotovi and 

 S. plumosum). The backward curve of the front border of the mesosoma, 

 however, reaching back to the dorsal ends of the bridle, is not found in any of 

 these other species. This characteristic feature, besides in S. japonicum, is 

 found in S. caulleryi, in the primitive Oligobrachia dogieli (p. 155) and also in 

 Nereilinum murmanicum. Another feature, moreover, which it shares in com- 

 mon with Siboglinum caulleryi appears to be the unsegmented tube with 

 simple rings, while the development of fibres in the walls closely recalls the 

 tube of S. pusillum. 



