424 THE EVOLUTION OF THE METAZOA 



The fact has already been known for some time and it has 

 been accepted by many zoologists, that there exist several 

 small groups of worm-like animals which somehow represent 

 the transition from the Annelida to the Eucoelomata which 

 consist of few segments only. These intermediate forms are 

 partly enterocoelic, partly ecterocoelic animals. Earlier this 

 group was frequently called the Gephyrea (the bridging ani- 

 mals). This grouping, however, was out of agreement with the 

 facts because it includes animals which clearly belong to the 

 Annelida ; these animals were called now the Gephyrea chaeto- 

 phora (Echiuroidea). These Echiuroidea have been classified 

 quite generally and rightly among the Annelida, usually as 

 one of their independent groups (as a class or even as a phylum 

 which is certainly an overvaluation). 



As regards the system of the remaining small groups which 

 are not at all or only partly segmented, and which possess at 

 the same time a perigastrocoele, we find above all that the 

 group Molluscoidea corresponds least to the natural facts, and 

 that its name has been least fortunately selected. We can see 

 that according to Grobben, the Molluscoidea (which are also 

 called Tentaculata in the parenthesis) consist of three classes, 

 i. e. the Phoronidea, Bryozoa (Ectoprocta), and the Brachio- 

 poda. These Molluscoidea appear immediately after the class 

 Mollusca within the phylum Protostomia (Zygoneura, accord- 

 ing to Hatschek). All these three classes have in reality nothing 

 in common with the Mollusca. This is a grouping which has 

 been introduced because of a lack of a better solution. Neither 

 is the correct position given to the Mollusca in this 

 system; the Mollusca are clearly primarily unsegmented ani- 

 mals, while at the same time the unsegmented character of the 

 Molluscoidea must be considered as a secondary phenomenon. 

 Fortunately enough we find that this name "Molluscoidea" 

 has fallen into disuse. 



A much better name has been proposed for this animal 

 group by Lang. He called them Prosopygia. The members 

 of the group which have thus become united under this name 



