DIPLOBRACHIA 371 



be defined by the following features : the fore-part of the body is distinctly 

 divided externally into protosoma and mesosoma; the protosoma carries 

 two to four free tentacles, which, to all appearances, are homologous with the 

 foremost tentacles of Heptabrachia and Oligobrachia ; the keels of the bridle 

 each consist of a cuticular axial rod, to which are attached, behind, a series 

 of cuticular rodlets; all the papillae of the metasoma have adhesive papillae. 



There are four species: Diplobrachia japonica Ivanov, D. belajevi Ivanov, 

 D. capillaris (Southward), and D. southwardae Ivanov. 



Type of the genus : Diplobrachia japonica Ivanov. 



Key for the identification of the species of the genus Diplobrachia 



1 (6) The whole front part of the metasoma bears adhesive papillae. There 



are usually two tentacles, sometimes three or four. 



2 (5) The keels of the bridle do not meet dorsally. The cuticular plaques 



in the front part of metasoma are 20-25/x across. 



3 (4) There are six to thirteen pairs of papillae in the metameric part of the 



metasoma, of which all but the anterior papillae bear round plaques. 

 There are two to four tentacles. The tube is segmented with three 

 irregular rings in each segment. 3. D. capillaris (p. 378). 



4 (3) There are not less than 18 pairs of papillae with oval plaques in the 



metameric section of the metasoma. There are two tentacles. The 

 tube is segmented, usually with seven very regular rings in each seg- 

 ment. 1. D. japonica (p. 371). 



5 (2) The keels meet dorsally. The cuticular plaques in the anterior part of 



the metasoma are about 12/x across. There are more than 20 pairs of 

 metameric papillae. There are two tentacles. The tube is ringed but 

 unsegmented. 2. D. belajevi (p. 376). 



6 (1) Paired adhesive papillae are absent from the frontmost region of the 



metasoma. There are three or four tentacles. The keels of the bridle 

 do not meet dorsally. The plaques on the papillae of the front part of 

 the metasoma are 25/x across. The tube is segmented, usually with 

 five rings in each segment. 4. D. southwardae (p. 381). 



/. Diplobrachia japonica Ivanov (Figs. 148-51) 

 Ivanov, 1960c: 6, 92, 93, 97, 220-3, 226, 263, Figs. 87, 148-51. 



The fore-part of the body is rather long. The length to breadth ratio, 

 depending upon the state of contraction, varies between 4-5 : 1 and 7 : 1. It is 



