GENERAL ZOOLOGY 



Fig. 12.9. The erect, branching colonial ectoproct, Buoula. 

 Zoological Society.) 



(Photograph courtesy New York 



The genus Bugula, members of which are abundant along our North 

 Atlantic coast, is representative of the arborescent marine ectoprocts (Fig. 

 12.9). The individuals of the colony, termed zooids, grow in double rows on 

 upright stalks branching from the original point of attachment of a single 

 free-swimming larva. Each zooid is encased in a cuticular skeleton, into 

 which the lophophore with its ring of ciliated tentacles may be completely 

 withdrawn. The anus is located upon a collar-like region just below the 

 lophophore and thus projects beyond the cuticular sheath when the lopho- 

 phore is extended. Attached to the external surfaces of the major zooids 

 are smaller, highly modified individuals termed avicularia. These resemble 

 birds' heads; their large "beaks" are highly mobile and are opened and closed 

 by powerful groups of muscles. By grasping and removing small objects with 

 which they come in contact, the avicularia presumably function to keep the 

 colony free of encrusting organisms. 



Internallv, the U-shaped digestive tract consists of a pharynx, a stomach, 

 a caecum, an intestine, and a rectum (Fig. 12.10). Bugula is a ciliary par- 

 ticulate feeder, and its microscopic food is drawn into the mouth and driven 

 into the pharynx by the action of the cilia. Here the food collects in masses 

 which are moved through the digestive tract by the coordinated contractions 

 of muscle fibers in the wall of the gut. Digestion occurs extracellularly, 

 chiefly in the stomach, caecum, and intestine. Products of digestion are 

 absorbed by the single-layered gastrodermal mucosa. Further transfer into 



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