BRYOZOA. 71 



CHAPTER II. 

 MOLLUSCOIDEA. 



Attached bilateral unsegmented animals, with crown of ciliated 

 tentacles or spirally rolled buccal arms; enclosed by a cell or by a 

 bivalve shell, the valves of which are dorsal and ventral: with a 

 simple ganglion or with several ganglia connected by a pharyngeal 

 ring. 



The two groups, Bryozoa and Brachiopoda, which are included in 

 the Molluscoidea were formerly placed amongst the Molluscs, to 

 which they do indeed present affinities. With the increase in our 

 knowledge of their developmental history, it appears more and more 

 probable, not only that the two groups are descended from an ances- 

 tral form common to them and the Annelids, but also that in spite 

 of the considerable differences between them in the adult state, they 

 are in reality closely related, a supposition which agrees with the 

 great resemblance of their larvae. Should this view of the close 

 relationship of the Brachiopoda, which are always solitary, with the 

 Bryozoa, which almost always form colonies, turn out to be well 

 grounded, then the tentacular crown and the simple ganglion of the 

 latter would be homologous with the spiral arms and subceso- 

 phageal ganglion of the former respectively. 



Class 1. BRYOZOA * = POLYZOA. 



Small animals usually united together to form colonies ; with 

 ciliated tentacular crown, horse-shoe-shaped alimentary canal and 

 simple ganglion. 



The Bryozoa owe their name to the moss-like dendritic appearance 

 of their colonies, on which the small individual zooids are arranged 

 in a regular manner. The colonies may, however, have a foliaceous 

 or polyparium-like form, or they may form crusts on the surface of 

 foreign objects. Solitary Bryozoa are rare exceptions (Loxosoma). 

 As a rule the colonies possess a horny or parchment-like, frequently 



*F. A. Smitt, "Kritisk forteckning ofver Skandinaviens Hafs-Biyozoer 

 Ofvers." Kongl. Vetensk. Abad. ForkandL, 1865, 1866, 1867. 



H. Nitsche, "Beitrage zur Kenntniss der Bryozoen." Zeit. fur miss. ZooL, 

 1869 and 1871. 



J. Barrois, " Recherches sur 1'embryologie des Bryozoaircd." Paris, 1877. 



