BUGULA TURRITA (A Sea-mat). 



Phylum VII, MOLLUSCOIDA; class i, POLYZOA; sub-class i, Ecxo- 

 PROCTA; order i, GYMNOL.EMATA. 



HABITAT. The Polyzoa or sea-mats are common in shallow coast- 

 waters the world over. They grow in short, bushy tufts or branching 

 colonies attached to rocks, piles, and other objects in the water. In a 

 superficial way the colonial masses resemble those of the Hydroid 

 polyps. 



Technical Note. If living specimens are available one may study them 

 to advantage in a dish of sea water. In most cases, however, the 

 student will have to depend upon preserved material. Place a small 

 branching portion of a colony in a watch glass full of water and 

 study by the aid of a hand lens or dissecting microscope. 



STRUCTURE. The following outline will serve as a guide in locating, 

 identifying, and observing the various parts: 



a) Each stem or branch is made up of a number of individual zooids 



arranged one above the other in a certain definite way. How 

 many vertical rows of zooids constitute the branch? How are 

 they arranged in the row ? As growth in the colony is by budding, 

 the younger zooids are those near the upper end of the branch. 



b) Note that these zooids are each enclosed in an elongated, trans- 



parent cup from which a portion of the animal protrudes if the 

 individuals were killed while they were in an expanded condition. 

 These cups or sheaths called zocecia are composed of chitin- 

 ized cuticle. Do you find any empty zocecia from which the zooids 

 have perished . In what portion of the branch would you expect 

 to find them . Look for short, blunt spines on the zocecia. 



Exercise i. Draw the portion of a colony you have been studying. Give 

 attention only to details of branching and arrangement of zocecia 

 on the stem. 



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