VERMES 



CLASS I. BRYOZOA OR POLYZOA 



The Bryozoa (Gr. fipvov, moss, and t,wov, animal), or Polyzoa 

 (Gr. iroXvs, many, and £a>of, animal), occur to some extent in 

 fresh water, but the majority are marine, living chiefly along 

 the shore and in relatively shallow water, though some have 

 been taken from considerable depths. With one exception 

 they produce colonies which to the naked eye are often strik- 

 ingly like the hydroid colonies. These colonies occur either 

 as encrusting masses on stones, sticks, seaweeds, or other ob- 

 jects, or as freely branching, dendritic structures, and are gen- 

 erally small, only a few centimeters in diameter; but in some 

 fresh-water species they grow to a di- 

 ameter of half a meter, and when these 

 get into the water supply of a city and 

 die, they become very objectionable. 

 Each individual in a colony has a 

 secreted, external covering or shell, 

 with an opening through which the 

 anterior portion of the body may be 

 protruded. This shell may be gelat- 

 inous, chitinous, or calcareous in 

 structure, and in one suborder there is , 



Fig. 118. Scrupocellaria ferox. 



a chitinous lid, or operculum, attached Vi, vibracuia ; magnified. (After 



. .1 i 11 4.1 .. 4.1 :c „ r U^ Allman, from Claus and Sedg- 



to the shell, so that the orifice may be wick . s Text-book ) 

 completely closed after the animal has 



withdrawn inside. In this same suborder in which the opercula 

 occur we find curious polymorphic individuals ; they are of two 

 kinds : the avicularia, which resemble strikingly the beak of a 

 bird ; and the vibracuia, which consist chiefly of a long, freely 

 movable lash (Fig. 118). The function of these structures is 

 not known. 



The lophophore, or crest of ciliated tentacles, is circular or 

 horseshoe-shaped and surrounds the mouth. In a few cases 

 it incloses the mouth and the anus, and individuals in which 

 this occurs are placed in the subclass Entoprocta. Their gen- 

 eral structure is much simpler than that of the majority of the 

 Bryozoa, which belong to the subclass Ectoprocta. The ali- 

 mentary canal is more or less U-shaped, and hangs suspended 



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