SIBOGLINUM LACTEUM 323 



YX133D). Similar glands are also present in long bands down the metameric 

 part of the trunk, between the dorsal ciliated band and the openings of the 

 internal glands of the papillae. Farther back, patches of glands are associated 

 with the other papillae of the trunk. About 75 pairs of poorly differentiated 

 papillae occupy the 7-5 mm of metameric region, and the remaining 27 mm 

 of the preannular region has only occasional small papillae and diffuse 

 patches of glands until 14 mm before the first girdle. Here there are two 

 enlarged papillae tipped by cuticular bars about 40/x long, and a similar 

 large papillae lies just in front of the first girdle (Fig. YX133G, H). In the zone 

 of the two enlarged papillae the dorsal epithelium is ciliated (Fig. YX133G). 

 As far as I am aware, cilia have not been noted in this region before, but 

 they occur in another species (undescribed) of Siboglinum from the Atlantic, 

 and may perhaps be found in others. 



The two girdles lie close together, the first consisting of two unequal parts 

 while the second is continuous round three-quarters of the circumference. 

 The toothed platelets are arranged in irregular double or triple rows (Fig. 

 УХ133Я). Each platelet is 15 to 18/x long and has a small group of a few teeth 

 at the anterior end and a larger group of teeth posteriorly (Fig. YX133C). 



The postannular region of the trunk occupies 15 mm of the tube and is 

 20 to 25 mm long, being closely coiled up. It bears small dorsal shields of 

 epidermal glands, not well differentiated, opposite fairly large papillae, 

 flanked by smaller papillae, so that there are 3 or 4 papillae opposite each 

 shield. The cuticular bars crowning the papillae are about 15/x long. 



The tube is 10 cm long and 0-27 mm wide. The walls are faint milky-white 

 in colour, transparent, soft, unringed and unsegmented. They are slightly 

 wrinkled on the outside (Fig. YX133^). The anterior end of the tube is 

 closed, as it can be in some specimens of S. atlanticum (Southward & 

 Southward, 1958). 



The specific name lacteum records the milky appearance of the tube and 

 the animal. 



This new species belongs to the sub-group of the genus Siboglinum which 

 contains S. atlanticum, S. taeniaphorum, S. arabicum, S. concinnum and 

 S. subligatum. These are species with epidermal glands in front of the bridle 

 and in bands behind the bridle and along the anterior metasoma. S. lacteum 

 resembles S. atlanticum in having a mid-ventral furrow from the base of the 

 tentacle to the point of the bridle, but differs from it in lacking a transverse 

 groove between proto- and mesosoma and in having only two enlarged 

 papillae instead of a large number. Other distinctive characters are the un- 

 ringed tube, the presence of a pretentacular furrow, the presence of pinnules 



