PSEUDOCOELOMATE AND MINOR EUCOELOMATE PHYLA 



coelomate forms, they mav well have evolved from an ancestral stock which 

 also gave rise to the rotifers. 



Minor Eucoelomate Phyla 

 THE PHYLUM ECTOPROCTA 



Members of the phylum Ectoprocta are permanently attached, bilateral 

 metazoans; most representatives develop extensive colonies, either arborescent 

 or encrusting. In their possession of circumoral tentacles, they bear a super- 

 ficial resemblance to coelenterate polyps and to entoprocts, and they have 

 been classified with both of these groups. Increased knowledge of their 

 structure has, however, revealed that the ectoprocts are of a higher grade of 

 organization than either entoprocts or coelenterates. 



Typically, each individual has a ciliated ridge surrounding the mouth and 

 bearing many tentacles. This ridge, the lophophore, is circular in marine 

 ectoprocts and horseshoe-shaped in the fresh-water types. This characteristic, 

 among others, is a basis for the subdivision of the phylum into two classes. 

 In all, the anus lies just outside the lophophore, and the digestive tract is 

 consequently U-shaped. This arrangement is not uncommon in sessile 

 metazoans. 



Fig. 12.8. An individual ento- 

 proct, Pedicellma cernua. This in- 

 dividual lias developed by the 

 metamorphosis of a larva. From 

 the base of its stalk a stolon is be- 

 ginning to form, which will grow 

 horizontally over the substratum. 

 From this stolon additional in- 

 dividuals will arise to form a 

 colony. (From C. Cori in W, 

 Kiikenthal and T. Krumbach, 

 1933, Handbuch der ^oolooie.) 



Collar 



Rectum 



Intestine 



Stomach 



Stolon 



Tentacles 



Collar 

 Mouth 



Ventral ganglion 



Basal disc 



357 



