MOLLUSCOIDA, TROCHELMINTHES, AND CHAETOGNATHA 



185 



movable jaws seem to serve as grappling hooks Avhich operate to 

 keep the colony free from other small organisms and debris which 

 may be present in the habitat. Yihramdaria (vibracula), which con- 



Esophaqus. 



-Jntestine 



Avicularium 

 / jaws open 



Muscle to body 

 wa// ' 



Muscle 



_run/cu/uj 

 (Mesentery) 



Ooecium 



Fig. 93. — Bugula, a marine bryozoan, showing the structure and habit of life of 



two zooids from a colony. 



stitute another modified type of zooid, are filamentous, whiplike 

 appendages. They are thought to be variations of the avicularian 

 modification. 



