SIBOGLINUM ATLANTICUM 263 



There is also a characteristic reduction of the anterior group of teeth on 

 the toothed platelets in both species and, moreover, both of them are among 

 the larger representatives of the genus. £. taeniaphorum is nevertheless 

 readily distinguished from S. atlantkum by the possession of 3 papillae in 

 the zone of thickening, arranged close together, one behind the other, by 

 the development of papillae in front of the girdles, by the lesser degree of 

 differentiation of the dorsal glandular shields in the postannular region of the 

 trunk, and by the fewer pairs of metameric papillae. S. taeniaphorum and 

 S. atlantkum undoubtedly form a close-knit group of species within the 

 genus Siboglinum, which makes it more remarkable that they should be so 

 isolated from one another geographically, since S. taeniaphorum comes from 

 near the Molucca Islands in the Pacific Ocean and S. atlantkum from the 

 Atlantic, near the coasts of Northern Europe. 



Material : 1 tube containing an intact animal. 



Locality: the western Pacific near the north coast of Morotai Island 

 (2°130'N 129°E) in the Molucca Islands. 



Depth : 260 m. 



24. Siboglinum atlantkum E. C. Southward and A. J. Southward 

 (Figs. 131-2) 



Southward, E. С and Southward, A. J., 1958b: 627-30, Figs. 1, 2; Ivanov, 1960a: 

 1531; Ivanov, 1960c: 4, 5, 14, 28, 98, 105, 128, 188, 190, 192-5, 197, 264, Figs. 87, 131-2. 



Recently E. C. Southward and A. J. Southward (1958b) described an 

 interesting species, S. atlantkum, which was found in the Atlantic Ocean to 

 the southwest of the British Isles, together with S. ehnani and S. inerme. 

 The material, consisting of 20 tubes, from which were extracted parts of 

 14 animals, was taken in 1957 and 1958 on cruises of R.V. Sarsia of the 

 Marine Biological Association of the United Kingdom, Plymouth. I was 

 able to become better acquainted with S. atlantkum through a well-pre- 

 served female specimen, the generous gift of Dr. Eve C. Southward. The 

 description given here is based on that of the Southwards, supplemented by 

 my own observations. 



The fore-part of the body is greatly elongated with a length to breadth 

 ratio of 9-12 : 1, and the protosoma and cephalic lobe together account for 

 only a fifth to a quarter of this (Fig. \Z\A). The large conical cephalic lobe, 

 pointed at the tip, is not divided from the protosoma, but between the 

 latter and the mesosoma runs a simple annular groove, interrupted on the 

 dorsal side. The rather stout, very long tentacle, attached at the bottom of a 



