456 PART II. SYSTEMATIC ACCOUNT 



Key for the identification of the species of Pogonophora 

 from their tubes* 



1 (74) The anterior part of the tube is flimsy, transparent, and very soft, 



with walls which collapse easily. 



2 (5) For a considerable length of the tube there is a peculiar external 



layer, supporting coarse, circular fibres, and removable with a 

 sharp scalpel. 



3 (4) The diameter of the tube reaches 1 mm. Under the dark fibrous 



layer the wall of the tube is a transparent dark brown, with light, 

 irregular, mainly transverse stripes Birsteinia vitjasi (p. 169). 



4 (3) The diameter of the tube is not greater than 0-5 mm. Under the 



muddy-brown fibrous layer, the wall of the tube has short, irregular 

 rings with light intervals between them. 



Heptabrachia subtilis (p. 342). 



5 (2) There is no external layer of circular fibres. If fibres are present 



they do not form a separate layer. Sometimes there is a superficial 

 felt-like layer. 



6 (65) The tube is ringed for most of its length. 



7 (24) Eye-catching brown circular fibres are present in the walls of the 



tube. 



8 (9) The rings of the tube are formed exclusively from agglomerations 



of thickened fibres. Siboglinum microcephalum (p. 227). 



9 (8) The rings of the tube consist of a dense substance, in which 



transverse fibres may run. 



10 (11) The rings are colourless or whitish, and transparent. Many rings 



are incomplete or irregularly shaped and anastomosing with one 

 another. Their edges are always even. The front part of the tube is 

 segmented, and reaches a diameter of 0-35 mm. 



Siboglinum taeniaphorutn (p. 257). 



11 (10) The rings are yellow or brown and more or less opaque. 



12 (13) The front part at least of the tube is segmented, with 6-7 rings per 



segment. The muddy-brown, regular rings are no longer than the 

 diameter of the tube, which is 0-17-0-22 mm thick. 



Diplobrachia japonic a (p. 371). 



* The following species have been omitted from this key: Oligobrachia ivanovi, Nereilinum 

 murmanicum, Siboglinum inertne, S. macro brae hium, S. debile, S. timorense, S. veleronis, S. subli- 

 gatum, S. concinnum, S. arabicum, S. silone, S. ceylonicum, S. exile, S. sumatrense, S. zanzibaricum, 

 S. sergeevi, S. lacteum, Siboglinoides dibrachia, Heptabrachia talboti, H. celebensis, H. ctenophora, 

 H. canadensis, Diplobrachia capillaris, D. southwardae, Sclerolinum sibogae, Polybrachia barbata, 

 Krampolinum galatheae, Galathealinum brachiosutn, G. arcticum and Lamellisabella minuta. 



