SIBOGLINUM MICROCEPHALUM 111 



very long postannular region carries a more or less regular series of metameric, 

 dorsal glandular shields (Fig. 115/)), but it has not been possible to study 

 these in detail because of the bad state of preservation. 



Measurements made on the two specimens yielded the following results : 

 length of the tentacle, not less than 9 mm; length of the anterior section of 

 the body, 0-62 mm, breadth, 0-12 mm; length of the preannular section of 

 the metasoma, <r. 15 mm; distance between the second and third girdles, 

 2 mm; length of the postannular section of the body, not less than 8 mm; 

 overall length of the body, including the tentacle, not less than 35-40 mm. 



The spermatophores are not known. 



The stoutish soft transparent tube has pronounced regular muddy-brown 

 rings, whose length is half the diameter of the tube or a little more. The 

 interspaces between the rings are large, completely transparent and colourless 

 (Fig. 115^). The diameter of the tube in the front half is 0-13 mm, and the 

 biggest fragment is about 20 cm long. 



S. buccelliferum belongs to the group of species with only one row of 

 pinnules, but it differs from the rest of this group in the absence of any 

 glandular patches on the mesosoma, in the dorsal fusion of the keels of the 

 bridle, in the development of three girdles, and in the possession of an annu- 

 lar groove immediately behind the base of the tentacle. This last feature, 

 however, it shares with S. pusillum. The spatulate, "buccellate" form of the 

 toothed platelets, with their strongly developed front group of teeth, is most 

 characteristic of S. buccelliferum. 



Material: 2 specimens. 



Locality: the northern part of the Coral Sea, near Treasury Island 

 in the British Solomon Islands (7°30'S 154°15'E). 



Depth: 960 m. 



13. Siboglinum microcephalum Ivanov (Figs. 116-17) 

 Ivanov, 1960c: 5, 96, 127, 160, 163-6, 167, 180, 197, 198, 264, Figs. 87, 116-17. 



Amongst the washings from a trial dredging taken by R.V. Vityaz* in 

 August, 1957, in the northern part of the Coral Sea at a depth of about 

 2000 m, was found a most distinctive tube of Siboglinum containing an entire 

 animal. At first glance even, it was obvious that this belonged to no known 

 species. Study of the external morphology confirmed this opinion. From the 

 most characteristic feature, the very small cephalic lobe, this species derives 

 its name, S. microcephalum. 



The rather long fore-part of the body, with a length to breadth ratio 



