Polyzoa. 



CHAPTEE XIII 

 POLYZOA 



{Phylactolaemata — Plumatella, Cristatella, Lophopus. 

 fCycloatomata— Crisia, Eomera. 

 Gymnolaemata J Ctenostomata — PaludiceUa,Alcyonidmm. 

 I Cheilostomata — Bugula, Memhranipora, 

 I Flui 

 Entoprocta — Loxosoma, PedicelUna. 



Characteristics. — Small coelomate animals, invariably possess- 

 ing the faculty of budding. The colonies nearly always fixed. 

 The ectoderm secretes, as a rule, a cuticle, which may be horny 

 or calcareous. The intestine is bent in the form of a \J, the 

 anus and mouth being approximated ; between them is situated 

 the nerve ganglion. The mouth is surrounded by a series of 

 ciliated tentacles. The individuals of the colonies may be 

 hermaphrodite, but the generative cells may ripen at different 

 times. 

 The Polyzoa comprise a very great number of species, which 



can be grouped into two main subdivisions : 



(i.) The Ectoprocta, in which the anus lies outside the circlet 



of tentacles which surrounds the mouth. 



(ii.) The Entoprocta, or those forms in which the circlet of 



tentacles or lophophore embraces both ends of the alimentary canal, 



the anus as well as the mouth. 



The latter subdivision contains very few forms, but the 



former includes a great number of species, mostly marine ; a 



few, however, inhabit fresh water. 



Plumatella fungosa is a fairly common representative of the 



freshwater Ectoprocta. It occurs all over Europe, on pieces 



of submerged trees, etc., living by preference in stagnant 



or slowly-flowing water. Each individual of the colony lives 



