CHAPTER 1 



Introduction 



Phylum POGONOPHORA BEKLEMISHEV, 1944 



(Synonyms: Phylum Pogonofora Ulrich, 1950; Phylum Brachiata Ivanov, 1955) 



The deuterostomic nature of the Pogonophora is amply indicated by their 

 general body plan and the enterocoelic mode of formation of the coelom. 

 The major body-axis of the pogonophora, as in the Enteropneusta, is homo- 

 logous with the axis of symmetry of protaxial animals. This is apparent from 

 the correspondence of the antero-posterior polarity of the body with that of 

 the egg. The archetypal 3-segmented plan has been preserved in the adult 

 structure of the Pogonophora and in this respect they are like the Hemi- 

 chordata and sharply distinguished from the remaining deuterostomate 

 phyla in which the primitive 3-segmental organization has undergone very 

 complicated transformations during the process of evolution (e.g. in the 

 Echinodermata and the Chordata). 



The chief peculiarities of the phylum Pogonophora, distinguishing them 

 from other Deuterostomia, are as follows : 



1. The development of tentacles on the first segment of the body; 



2. The possession of coelomoducts in the first and third segments; 



3. The primitive close connexion of the gonad with the coelom; 



4. The development of a distinct heart on the ventral blood-vessel; 



5. The complete suppression of a gut in the adult structure; 



6. The strong cuticularization of the integument; 



7. The profound secondary modification of embryonic development. 



In the phylum Pogonophora there is only one class, the class Pogonophora. 



Historical survey 



The honour of the discovery of the first pogonophore belongs to the 

 eminent French zoologist Maurice Caullery, who, in 1914, described 

 material collected by the Netherlands Siboga Expedition in the seas of the 

 Malayan Archipelago. He lumped the whole of this material together under 

 the name Siboglinum weberi [the expedition was led by M. Weber] when some 

 thirty years later, in 1944, he published a monograph on S. weberi in which 



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