10 



PART I. GENERAL ACCOUNT 



ч-4 -S' 



f 



mts 



possess a complete specimen, is probably 

 larger than either, attaining a diameter of 

 1 -5 mm and a length of some 30-45 cm.] 



The bodily proportions are extraordinary. 

 One of the features of the Pogonophora 

 which strikes one at first glance is the unus- 

 ual elongation of the body (Fig. 2). The length 

 is always at least 100 times the breadth. Thus 

 in Siboglinum caulleryi the length to breadth 

 ratio may be 600:1, in S. minutum 550:1, in 

 Oligobrachia dogieli 400:1 and in Hepta- 

 brachia subtilis 200:1. One of the species 

 which is least elongated — Spirobrachia bek- 

 lemischevi — has a body which is at least 100 

 times as long as broad. 



The small and medium-sized forms are 

 semi-transparent, almost colourless or whit- 

 ish. The circulatory vessels may be seen 

 through the body wall filled with red blood, 

 which gives the tentacles a rosy-pink or red 

 hue. In the males the whitish mass of the 

 genital system may usually be seen in the 

 anterior part of the trunk and in the post- 

 annular region, while in the females the 

 yellowish yolky eggs may be seen in the front 

 part of the preannular region. The large 

 Spirobrachia grandis is distinguished by the 

 brick-red colour of the body. [The glandular 

 patches of epidermis on the mesosoma of 

 Siboglinum inerme and some other species 

 of this genus are whitish in the living animal 

 and the cephalic lobe is brownish.] 



Fig. 3. The front part of the body of Siboglinum caulleryi, 

 viewed from the left side and somewhat ventrally. 

 с - cephalic lobe ; f- bridle (frenulum) ; tns - mesosoma ; 

 . ну mts - metasoma ; pa - papillae ; pi - pinnules ; ps - pro- 

 tosoma ; s 1 - groove between the protosoma and mesosoma ; 

 s 2 - groove between the mesosoma and the metasoma ; 

 sv - ventral sulcus ; / - tentacle ; vv - ventral blood vessel 

 seen by transparency. (After Ivanov, 1957a.) 



