S1B0GLINUM ATLANTICUM 



267 



The rings of the pale brownish-grey unsegmented tube are no longer than 

 a third the diameter of the tube, and for the most part possess even edges, 

 but often one may encounter rings irregularly shaped or with uneven edges. 

 The intervals between the rings are transparent and transversely wrinkled, 

 but free of fibres (Fig. 132Д B). The front and hind ends of the tube are 

 transparent. The longest tubes are 32 and 40 cm long. As noted by Southward 

 and Southward they have one very distinctive feature, in that they are 

 narrower in front than in the middle, in total contrast to the usual even 





В 



Fig. 132. Siboglinum atlanticum: Tube: A - front part; В - middle part. 



backward taper: the diameter in the front part of the tube is с 0-42 mm, 

 and in the middle part 0-5 mm. 



S. atlanticum is undoubtedly very closely related to S. taeniaphorum 

 (pp. 263 and 259), but distinguished from it in a number of ways: by the 

 two rows of pinnules, by the numerous, disorderly papillae of the zone of 

 thickening (S. taeniaphorum has only three), by the bigger and broader 

 toothed platelets, whose anterior group of teeth are not rudimentary, by the 

 development of cuticular plaques on the papillae of the zone of thickening 

 and on those of the postannular region, and, finally, by certain features of the 

 tube, especially its lack of segmentation. 



