SIBOGLINOIDES 331 



We have already noted that Siboglinoides is much nearer to Siboglinum than 

 to Nereilinum. The characters which distinguish Siboglinoides from Nereilinum 

 are as follows : in Siboglinoides the absence of the deep backwards dorsal 

 sweep which the groove between the protosoma and the mesosoma makes in 

 Nereilinum, the absence of a glandular girdle behind the bridle and of the 

 masses of glandular cells from the epidermis of the anterior part of the trunk, 

 the presence of four or five girdles arranged in two groups, the strong develop- 

 ment of the anterior groups of teeth on the toothed platelets, the presence of 

 flask-shaped glands in front of the bridle and the presence of pinnules on the 

 tentacles. Perhaps the most important distinction is that Siboglinoides has 

 fully developed secondary metamerism of the papillae of the anterior part of 

 the metasoma, while metamerization of this region has hardly begun in 

 Nereilinum, and there are not even any distinct papillae. Since the lack of 

 papillae and of secondary metamerization of the anterior part of the trunk are 

 characteristic of the family Oligobrachiidae, it is evident that Siboglinoides 

 must be placed in the family Siboglinidae. 



Material : six tubes of which one was empty. 



Localities: Timor Sea to the south-west of Roty Island (11°30'S, 122° 

 30'E); Indian Ocean south of the Straits of Bali (9°05'S, 114°14'E); south 

 of Java (8°56'S, 108°22'E); the western part of the Arabian Sea to the 

 north-west of the Island of Socotra at the entrance to the Gulf of Aden 

 (12°48'N, 52°38'E). 



Depth: 2080 m to 3300 m.] 



2. Order THECANEPHRIA IVANOV, 1955 



In the Thecanephria the first coelom is horseshoe shaped, but in the 

 Spirobrachiidae its right half is somewhat drawn out and twisted into a 

 corkscrew, in correlation with the development of the spiral lophophore. 

 The excretory sections of the coelomoducts of the protosoma approach the 

 boundary of the mesosoma in the median plane, where they lie in sac-shaped 

 ventral extensions of the dorsal blood vessel. The tentacles are sometimes 

 fused together. The postannular region of the metasoma has transverse 

 ventral adhesive papillae, bearing cuticular plaques, but it has no dorsal 

 glandular shields. The spermatophores are more or less leaf-shaped. The 

 tube may be ringed or segmented, its front part either filmy, or ending in a 

 hard, funnel-shaped mouth. 



The order Thecanephria has three families: Polybrachiidae, Lamellisa- 

 bellidae and Spirobrachiidae, of which the first is the most primitive. 



