SIBOGLINUM SERGEEVI 



321 



ends fuse (Fig. YY133y4). No flask-shaped gland has been observed in 

 the mesosomal region. Except for a forward excursion in the mid-dorsal line, 

 the groove between the mesosoma and metasoma is simple (Fig. YY133i?). 



The very front end of the metasoma lacks papillae. For some 0-5 mm 

 the deep ventral sulcus is bounded only by smooth lateroventral ridges 

 (Fig. YY133^4). The broad dorsal ciliated band, however, begins at the 

 very front edge of the metasoma (Fig. YY133B). When the metameric 

 papillae finally begin they are small, rounded, tightly-packed and plaqueless, 

 and each contains a single pyriform gland (Fig. YY133y4). Towards the 

 caudal end of the region, where they become less regular, their size increases 

 a little. There are 15 papillae on the left and 16 on the right. 



The nonmetameric part of the trunk is approximately twice as long as the 

 metameric (Fig. XX133). It bears scattered papillae and glandular patches 

 of epidermis, the latter especially on the dorsal side. In the zone of thickening 

 there is only one large conical plaqueless ventral papilla (Fig. XXI 33). 

 It is situated almost in the middle of the nonmetameric region, indicating 

 that the front half of the preannular region is somewhat underdeveloped — 

 a sign of the immaturity of our specimen. 



There are two girdles, both broken on the ventral side (Fig. XX133). At 

 the level of the first girdle there is a small ventral papilla and a second larger 

 one lies behind the second girdle. Both lack either plaques or cuticular thicken- 

 ings at their tips. The girdles lie on broad protuberant ridges (Fig. YY133Z)). 

 The toothed platelets, narrower at the 

 front end, are arranged in one row (Fig. 

 ZZ133^4). The anterior group of teeth 

 is feebly developed (Fig. ZZ1335). 

 The platelets are 14-18/z long. 



The postannular section is almost 

 the same length as the preannular, but 

 considerably thinner and it tapers 

 gradually towards the hind end of the 

 body (Fig. XXI 33). It bears meta- 

 meric dorsal glandular shields which 

 are shaped like buttons (Fig. УУ133£), 

 or else stretched out irregularly side- 

 ways (Fig. XX133). A tongue-like 

 transparent plaqueless ventral papilla 

 is situated opposite each shield (Fig. F > 22.Ш. Siboglmum sergeevi: A -part 

 \rvm гл of a girdle; В - toothed platelet, da-an- 



1 I 1 j SL). terior group of teeth; dp - posterior group. 



