SIBOGLINUM FRENIGERUM 213 



9. Siboglinum frenigerum Ivanov (Fig. 110) 



Ivanov, 1960c: 5, 12, 96, 125, 145, 148, 151-3, 186, 196, 264, Figs. 87, 110. 



This species was taken, together with S. buccelliferum and S. robustum, 

 near Treasury Island, in the northern part of the Coral Sea, at a depth of 

 960 m, in January, 1957 by R.V. Vityaz\ Two females were collected, both 

 with characteristic white ringed tubes, at first glance recalling those of 

 S. cinctntum and S. vinciilatam. Another female was taken by R.V. Vityaz? in 

 November, 1959, in the Indian Ocean off the south coast of Sumatra. The 

 extraordinarily strong development of the keels of the bridle affords grounds 

 for naming this species S. frenigerum [Latin frenum, a bridle, gerere, to bear.] 



The length to breadth ratio of the fore-part of the body is 7 : 1. In front of 

 the bridle are 2 simple annular grooves, the first being half-way between the 

 tentacle and the hind groove (Fig. ПОЛ, B). The blood vessels in the large 

 conical cephalic lobe are readily visible by transparency. The basal part of 

 the very long, comparatively stout tentacle, which is attached in the mid- 

 ventral line, is free of pinnules (Fig. 1105). More distally, pinnules about 

 0-07 mm long, are attached rather sparsely in a single row, but with a slight 

 tendency to form a double row (Fig. HOC). The muddy-brown, very broad 

 keels of the strongly pronounced bridle are fused together both dorsally and 

 ventrally and reach their greatest thickness at the sides of the body (Fig. 

 ПОЛ, B). The ridges of the bridle are particularly well-developed on the 

 ventral side. Behind the bridle is a protuberant glandular girdle, interrupted 

 both ventrally and dorsally, and between the bridle and this girdle a weak 

 constriction is discernible, forming a sort of waist. The back edge of the 

 mesosoma is curved on the ventral side. 



The metamericj>art of the trunk is a little narrower than the mesosoma and 

 the papillae here are rather large, each with a pyriform gland visible inside it. 

 Farther back they become somewhat drawn out and elongated. There are 60- 

 64 pairs of metameric papillae. The dorsal ciliated band is much as usual 

 (Fig. ПОЛ). Behind the female genital apertures, in the region of the 

 thickened papillae, are 13-16 large conical transparent papillae arranged in a 

 more or less ventral row. On the tip of each one lies a very small thickening 

 of the cuticle — a sort of rudimentary plaque (Fig. 110Z)). Then, between the 

 zone of thickened papillae and the girdles, the trunk bears numerous darkish 

 warts of a glandular character, placed higgledy-piggledy (Fig. 110£). Of the 

 two girdles, which lie close together (Fig. HO/% G), the first is weakly 

 developed and arranged as a pair of oblique lateral half-hoops, not meeting 

 either dorsally or ventrally, while the second, lying on a broad ridge, is 



