Phylum Molhisca and Minor Eucoelomate Phyla 483 



individuals, each of which is less than a millimeter in length. Each 

 zooid consists of a chitinized tube, the cooecium enclosing the polypide 

 or internal parts. The anterior end consists of a horseshoe-shaped ridge, 

 the lophophore, which bears a row of ciliated tentacles which in turn 

 surround the mouth. The lophophore is attached to an opening in the 

 zooecium by a chitinized collar. The whole lophophore area may be 

 withdrawn within the zooecium by powerful retractor muscles. On the 

 outside of the zooecium of many individuals is a structure shaped like 

 a bird's head and known as the avicularium. It has two powerful jaws 

 which are able to open and shut and keep the outside free of encrusting 

 forms which might settle on the surface. The mouth opens into the 

 pharynx which in turn opens into the esophagus and then a U-shaped 

 stomach, and finally a slender intestine leading to the anus. The whole 

 tract is lined with cilia. There is a large retractor muscle, the funiculus, 

 which acts to pull the stomach away from the mouth. There is a large 

 nerve ganglion below the lophophore which sends out nerve fibers to the 

 various parts of the body. There is no circulatory, excretory, or special 

 respiratory system. Since Bugula is monoecious both ovaries and testes 

 develop in the same individual. These develop from the lining of the 

 coelom. The area in which the eggs of the ovary develop forms a 

 brood pouch, the ooecium. All these structures are enclosed within the 

 body cavity which has a true peritoneal lining. 



The fertilized egg develops into a trochophore larva. This swims 

 about for a while and then settles down and asexually produces a new 

 colony. 



Most of the bryozoans feed on floating microscopic organisms which 

 are carried to the mouth by currents set up by the tentacles. The small 

 particles are entangled in mucus and then swallowed. The powers of 

 regeneration of the members of this group are startling. At times all 

 the parts within the zooecium degenerate to form a broivn mass. A 

 new body forms, and the brown mass lies on the stomach of the new 

 individual. Later it is expelled through the anus. 



The fresh-water bryozoans have some interesting structures asso- 

 ciated with the viscissitudes of their environment. To survive un- 

 favorable winter conditions, they develop asexual buds known as stato- 

 blasts (Fig. 159,5). The cells are formed on the funiculus and are 

 surrounded by a chitinized shell. They are released when the old colony 

 dies. The outer layer of these statoblasts is porous and collects air 

 which enables them to float for a period of time. 



