CHAPTER 11 

 The Tube 



The tube of Pogonophora is never branched. It is almost cylindrical, 

 though usually tapering very slowly indeed from the front end backwards. 

 [An exception is Siboglinum atlanticum which is wider than anteriorly 

 (Southward and Southward, 1958 — D.B.C.]. Its length is several times 

 the length of the animal, varying from 15-20 cm in the smaller species of 

 Siboglinum to 150 cm in Zenkevitchiana longissima. The diameter varies 

 from 0.1 mm in Siboglinum minutum and S. tenue to 2.8 mm in Spirobrachia 

 grandis. 



The structure and general nature of the tube are essentially similar in all 

 Pogonophora. The tubes of Siboglinum, Oligobrachia, Diplobrachia and some 

 other genera are pliable and comparatively soft, Zenkevitchiana has a parch- 

 ment-like, whitish elastic tube and Polybrachia, Lamellisabella and Spiro- 

 brachia grandis have very rigid thick-walled brown or black tubes. Details of 

 the structure of the tube often serve well for specific diagnosis. 



The tube may be uniform along its whole length or consist of very close 

 dense rings alternating with clear elastic interspaces (Figs. 84^4, 85). The 

 rings may be equal and regular {Siboglinum caulleryi, Oligobrachi dogieli 



1 6 



Ei 



Fig. 84. Tubes of various Pogonophora: A - Siboglinum fedotovi; В - Lamellisabella johanssoni; 

 С - Polybrachia annulata; D - Spirobrachia beklemischevi. (After Ivanov, 1957a.) 



120 



