THE INVERTEBRATE PHYLA 



107 



are certain real resemblances between the animals at the base of 

 the Protostomia and the base of the Deuterostomia. Thus the 

 Ectoprocta and the Pterobranchiata have a body that is in three 

 segments; the Ectoprocta and Brachiopoda are enterocoelic, the 

 Ectoprocta have coelomic pores and budding is often similar in 

 pattern. 



The first major division within the Protostomia is the Tenta- 

 culata, which is comparable to the Molluscoidea of Grobben. 

 Of these the Phoronidea are considered as being the most primitive 

 whilst the Entoprocta are considered to be derived from attached 

 larvae of the Ectoprocta. 



The Nemertea are coelomate, their coelom being restricted to 

 the rhynchocoel and the gonad cavities. The nemerteans are more 

 primitive than the Turbellaria since they have an anus and their 





Aschelminthes 



f Arthropodo I 



V. v J 



^Annelida A, || usca 



Platyhelminthes 

 Nemertini 



Fig. 37. Marcus's classification of the Invertebrate Phyla. 



