BUGULA 69 



SUBPHYLUM BRYOZOA 

 BUGULA 



Bugula turrita is a marine colonial bryozoan which is very com- 

 mon in the shallow waters along our coast. The colonies are a 

 dull yellow in color and sessile, being attached to rocks, seaweed, 

 and other objects. The animals are very small and must be 

 studied with the aid of a microscope. 



Study a large piece of a colony (alive if possible) and notice the 

 spiral arrangement of the branches. A branch is made up of a 

 double row of elongated partitions or chambers, each of which is 

 called a zooecium. Each zooecium represents a separate individual 

 of the colony ; within its walls are the soft parts of the animal, 

 which are called collectively the polypide. The individual bryo- 

 zoan is thus made up of two distinct parts, the zooecium and the 

 polypide, the former constituting the chitinous outer wall of the 

 animal, the latter comprising its viscera and the tentacles. At its 

 upper, or distal, end the zooecium has a large opening through which 

 the forward end of the polypide can be protruded and into which 

 it withdraws itself when alarmed. The cuticula which forms the 

 zooecium is rendered hard by the presence of carbonate of lime ; 

 it is thus much more enduring than the remainder of the animal, 

 and after death the empty zooecium may persist long after all the 

 softer parts have disappeared. Look for the empty zooecia in 

 your specimen. 



The different individuals of a colony have arisen by a process 

 of budding from the individuals below them in the colony. Thus 

 the oldest individuals are those nearest the base of the colony, 

 the basal one being the progenitor of the entire colony. This is 

 also the only individual of the colony which has not come into 

 existence by a process of budding ; it began its life as a free- 

 swimming larva which was hatched from an egg. 

 ■ The Zooecium. Mount a small portion of the colony containing 

 two or three branches on a slide under a cover glass. 

 Exercise 1. Draw a large and accurate outline of the zooecia, leaving 

 ' ' out the polypides. Observe very carefully the boundaries of the 

 zooecia and their relations to one another. 



