218 PART II. SYSTEMATIC ACCOUNT 



and subject to very great individual variation, and their number fluctuates 

 between 50 and 75 pairs. In the males the large genital papillae are promi- 

 nent (Fig. 11 1С). Farther back the ventral sulcus vanishes and the papillae 

 become smaller and move onto the sides of the trunk (Figs. 8, 112^4). Then 

 they quickly become larger again and move onto the dorsal side, at the same 

 time losing any trace of metameric arrangement (Figs. 8, 112^4). The 

 character of the trunk hardly changes after this until the girdles are reached, 

 except that at a considerable distance in front of them, in the zone of 

 thickened papillae, are located five prominent long tongue-shaped soft 

 papillae, closely spaced in a short median row on the ventral side (Fig. 10). 



The number, shape, arrangement and dimensions of the nonmetameric 

 glandular papillae are all subject to very great individual variation. Indeed, 

 it is literally impossible to match any two individuals which might be identical 

 in all these respects. In particular, between the zone of the median ventral 

 papillae and girdles, in many individuals the dorsal papillae are laterally 

 elongated, while in others this is not so. The two girdles (Figs. 12, 1125, C), 

 lying on well-developed muscular ridges, are both interrupted on the ventral 

 side and the first on the dorsal side also. In front of the girdles are two rather 

 large conical papillae, lying on the ventral side in the mid-line, one behind 

 the other, while a similar ventral papilla lies behind the girdles. The soft 

 transparent toothed platelets, arranged in two dense rows (Fig. 112Z)), are 

 faintly tinged yellow and noticeably constricted in the middle. The whole 

 surface of each platelet is covered with numerous, very small teeth, of which 

 the front group, covering less than one-third of the platelet, is divided from 

 the hind group by an obvious transverse line (Fig. 112£), just as in the 

 platelets ofS.fedotovi and S. robustum (Figs. 1017 7 and \21E). The platelets 

 measure 15-20/x long by 4-5/x broad. The postannular region of the trunk is 

 very long, as a rule considerably longer than the preannular region and 

 sometimes exceeding it two-fold. Towards the hind end it tapers impercep- 

 tibly, and at more or less equal intervals along it are situated large glandular 

 dorsal shields (Fig. 8), with a protuberant cushion-like papilla opposite 

 each one on the ventral side. The first dorsal shield, which varies in size, 

 is placed right behind the hindmost girdle (Fig. 1125). In general each 



Fig. 112. Siboglinum caulleryi: A - trunk in the transitional region between the metameric and non- 

 metameric portions, mainly in dorsal view, with part twisted to show the ventral side; В - region 

 of the girdles in dorsal view ; С - the same from the ventral side ; D - part of a girdle ; E - toothed 

 platelet (only the bases of the teeth indicated). 



an - girdles ; со - dorsal ciliated band ; da - anterior group of teeth ; dp - posterior group of teeth ; 

 pa - papillae ; pan - postannular region ; sc - dorsal glandular shield ; vd - dorsal blood vessel seen 

 by transparency. (В, С after Ivanov, 1957a.) 



