SIBOGLINUM FEDOTOVI 195 



three new specimens. As in related species (S. hyperboreum, S. robustum, etc.), 

 the first two are placed close together at a considerable distance from the 

 third, the first girdle is interrupted ventrally, the second dorsally and the 

 third both ventrally and dorsally, so that it consists of two half hoops. The 

 dorsal ends of these half-hoops sometimes turn forwards and outwards, while 

 the ventral ends may hardly reach round the sides of the body on to the belly 

 (Fig. 101D, E). All the girdles lie on muscular folds, and in each of them the 

 toothed platelets are attached in a single irregular row. In contrast with the 

 bigger Pogonophora, the transparent yellowish toothed platelets of this 

 species are broader at the front instead of the hind end (Fig. 1017 7 ). They are 

 further remarkable in that the anterior group of teeth is twisted round 

 obliquely almost as much as the posterior group (Fig. 101G). The anterior 

 teeth are more broadly based than the posterior, but shorter and fewer, and 

 between the two groups a transverse groove may be noticed dividing the 

 platelet into two equal parts, the anterior broader and the posterior narrower 

 (Fig. 10 IT 7 ). Most of the platelets are between 17 and 23/x long, but occa- 

 sionally one may see under-developed ones only 13-15/x long. At the very 

 beginning of the postannular region, on the ventral side, lie a few small, 

 transverse, adhesive plaques, shaped like brackets (Fig. 101£). 



The tentacle is 12 mm long, the anterior section of the body 1-1-1 -7 mm 

 long and с 0-2 mm broad. The preannular region may be up to 65 mm long, 

 but in one mature individual it was only 6 mm. 



The very characteristic spermatophores (Fig. 65A) are cigar-shaped, 

 broader at one end than the other. From the broader, rounded end runs the 

 delicate filament of the spermatophore. The peripheral region of the sperma- 

 tophore is cut off from the central region as a sort of cortex, free of sperm. 

 The length is 0-2 mm. 



A considerable length of the front part of the tube is transparent and 

 colourless, with very soft, limp membranous walls and clear segmentation. 

 Soon very soft, brownish rings begin to appear, 12-17 or even 18 per 



Fig. 101. Siboglinum fedotovi: A - front part of the body of a male in ventral view; В - the same 

 from the dorsal side; С - part of the tentacle; D - the posterior girdle and the front part of the 

 postannular region in dorsal view; E- the same from the ventral side ; F - part of a girdle of toothed 

 platelets ; G - toothed platelet from the side. 



an - girdle of toothed platelets; с - cephalic lobe; ei - glandular girdle; со - dorsal ciliated band; 

 da - anterior teeth; dp - posterior teeth;/- keel of the bridle; go - genital papilla; ms - mesosoma; 

 p - cuticular plaques; pa - papillae; pan - postannular region; pi - pinnules; ps - protosoma; 

 s 1 - groove between the protosoma and the mesosoma ; s 2 - groove between the mesosoma and the 

 metasoma; s 3 - pretentacular groove; so - ventral sulcus; t - tentacle; vd - dorsal blood vessel seen 

 by transparency; vv - ventral vessel seen by transparency. (A, B, C, D, E- after Ivanov, 1957a.) 



