124 PART I. GENERAL ACCOUNT 



adapted exclusively to these hadal depths. Heptabrachia abyssicola, H. 

 subtilis, Cyclobrachia auriculata, Diplobrachia japonica, Zenkevitchiana 

 longissima, Lamellisabella johanssoni and Spirobrachia beklemischevi are typical 

 hadal species. The greatest depth at which pogonophores have been found 

 is 9735 m. 



Besides the species of Pogonophora which have been described, we have 

 available abundant material collected in recent years by the Soviet expedition 

 of R.V. Vitya£ and R.V. Ob\ including another thirty or so species, largely 

 of the genus Siboglinum. It is not practicable to describe these species 

 because of the fragmentary nature of the material, but we can obtain a general 

 picture of their vertical distribution, as follows: 17 of these nondescript 

 species inhabit depths greater than 3000 m. Eight of these were taken in 

 depths between 5000 and 9000 m. Eleven species were found at depths less 

 than 3000 m. All these animals were taken on a muddy bottom. 



Pogonophora lead a sedentary tubicolous life and other animals may settle 

 on the stiff very long tubes of such species as Lamellisabella zachsi and 

 Polybrachia annulata. Foraminfera, siliceous sponges, hydroids, alcyonarians, 

 small actinians (Hormathiidae), serpulids, bryozoans, ascidians and even 

 stalked sea lilies have been found attached in this way, and the chitin-like 

 cup-shaped scyphistoma colonies of Stephanoscyphus are especially common 

 [the scyphistoma stage of Nausithoe - Coelenterata Scyphozoa Coronatae]. 

 The characteristic localization of these epibionts indicates that a considerable 

 part of the pogonophoran tube projects freely above the surface of the seabed, 

 arranged more or less vertically, while the remaining basal part is apparently 

 deeply submerged in the sediment. The soft flimsy tubes of species of Sibo- 

 glinum and the elastic white tubes of the hadal Zenkevitchiana have no epi- 

 bionts and are apparently almost wholly submerged in the sediment. 

 [Marks on the tube of Siboglinum spp. have been interpreted by Southward 

 and Southward (1958b) as marking the level of the surface of the mud, and 

 it is possible that the anterior ends of these tubes lie more or less flat on the 

 surface of the sediment — D.B.C.] 



Pogonophores probably form dense stands. This follows from their lack 

 of a pelagic larva. [It is also confirmed from the quantitative haul of Hartman 

 (1961) and the work of A. J. Southward (1958)]. 



Pogonophora are frequently numerous and very characteristic organisms 

 of benthic biocoenoses. Thus in the northwest part of the Sea of Okhotsk the 

 coastal shallow-water stretches of muddy bottom (depth 90-200 m) are 

 densely occupied by Siboglinum caulleryi. In the Bering Sea between depths 

 of 1400 and 5000 m Polybrachia annulata frequently appears to predominate 



