SIBOGLINUM FRENIGERUM 215 



interrupted only on the ventral side (Fig. HOT 7 ). The toothed platelets of each 

 girdle, arranged in two irregular rows (Fig. ПОЯ), are yellowish elongated 

 ovals, covered with comparatively large teeth pointing forwards. The teeth 

 of the anterior group are poorly developed and few in number (Fig. 1107). 

 The platelets measure 10— 11/x by с. 3/л. The anatomy of the postannular 

 trunk has not been investigated. 



All the known animals are females of almost identical size, and their 

 dimensions are as follows : length of the tentacle, up to 6 mm ; length of the 

 fore-part of the body, 0-67 and 0-75 mm; breadth of the mesosoma, 0-1-0T5 

 mm ; length of the preannular region of the trunk, 27 to 46 mm ; length of the 

 postannular region up to 33 mm. The overall length of the body, including 

 the tentacle, is not less than 86 mm. 



The ringed tube is distinguished by its whiteness. The very regular, lack- 

 lustre rings, a little shorter than the diameter of the tube, are colourless or 

 slightly mud-coloured, and the narrow colourless intervals between them 

 are smooth and glassily transparent (Fig. 110/). In all individuals the 

 remaining fragment of tube was almost 20 cm long, with a diameter of almost 

 0T7 mm near the front end. 



The characteristic features of the species are as follows : the two simple, 

 annular grooves between the base of the tentacle and the bridle, the "waist" 

 behind the bridle, the extraordinarily strongly developed keels of the bridle 

 (in this respect S.frenigerum is different from all other species ofSiboglinum), 

 the fifteen or so conical papillae of the zone of thickening, the two girdles, 

 each with two rows of platelets, the considerable reduction of the front 

 group of teeth on the platelets of the girdles, and the whiteness of the 

 tube. 



Material : three almost complete females. 



Locality: The Coral Sea near Treasury Island in the British Solomon 

 Islands (8°S 155°E) and off the coast of Sumatra. 



Depth: 620-960 m. 



Fig. 110. Siboglinum frenigerum : A - front part of the body of a female from the dorsal side ; В - the 

 same in ventral view ; С - part of a tentacle ; D - zone of thickened papillae from the right side ; 

 E- part of the trunk in front of the girdles in ventral view; F - girdles from the ventral side; 

 G - the same from the dorsal side; H - part of a girdle of toothed platelets; /-toothed platelet; 

 jf -tube. 



an - girdles; с - cephalic lobe; ci - glandular girdle; со - dorsal ciliated band;/- keel of the bridle; 

 ms - mesosoma; p - cuticular plaque; pa - papillae; pi - pinnules; ps - protosoma; s 1 - groove 

 between the protosoma and the mesosoma ; s 2 - groove between the mesosoma and the metasoma ; 

 s* - post-tentacular groove; sv - ventral sulcus; t - tentacle; vv - ventral blood vessel seen by 

 transparency. 



