CHAPTER 14 



Systematic Position of the Pogonophora and Evolution 

 within the Class 



Are they related to the Annelida ? 



All the studies of the organization of the Pogonophora which have been 

 published in recent years (Caullery, 1944; Ivanov, 1952, 1955a, b, c, 1957b, 

 1958a, b, 1960a; Jagersten, 1956, Johansson, 1937, 1939) do not leave any 

 doubt of their oligomerism, or, more precisely, of their trimerism. It is not 

 surprising, therefore, that all zoologists who have deliberated upon their 

 systematic position have begun from the premise of their oligomeric nature 

 (besides the above authors I might mention: Reisinger, 1938; Ushakov, 1940, 

 1953; Hempelmann, 1943, Beklemishev, 1944, 1951, 1952, 1957, 1958; 

 Dawydoff, 1948; Ulrich, 1950; Boettger, 1952; Dogel', 1954, 1960; Zenke- 

 vich, Birshtein and Belyaev, 1954; Abrikosov et al, 1955; de Beer, 1955; 

 Petrunkevitch, 1955; Kirkegaard, 1956a; Alvarado, 1957a, b; Borradaile, 

 Eastham, Potts and Saunders, 1958; Manton, 1958; Southward and South- 

 ward, 1958b). The only exception has been Hartman (1954), who looked 

 upon the Pogonophora as polychaetes, regarding them as having changed 

 from a polymeric structure to oligomerism by way of reduction of the dissepi- 

 ments under the influence of a tubicolous way of life. In her opinion the 

 adhesive papillae of Pogonophora were nothing but a variety of parapodia 

 and their cuticular plaques corresponded to parapodial setae. 



There is no need to go into a lengthy critique of these ideas.* Their 

 complete inadequacy is clear from all the fore-going discussion. Neither in 

 their basic body plan nor in their embryological development do the Pogono- 

 phora show anything in common with the Annelida. 



And if that is so, then the question arises of how we are to regard the 

 similarities with the annelids, which are undoubtedly present in some 

 details of the organization of pogonophores. Amongst such morphological 

 traits we may mention the toothed platelets of the girdles, the provisional 

 bristles of the embryo and some features of the genital system. 



The external similarity of the toothed platelets on the girdles of Pogono- 

 phora to the uncini of sedentary polychaetes, first noticed by Caullery (1944), 

 can easily be explained by their similar mode of life. Cuticular hooks and 



* Such a critique is given by Ivanov (1955b, c). 



132 



