CHAPTER X 



BRYOZOANS 



Bryozoa (or Polyzoa) 



Form and habits of bryozoans. — Bryozoans look so much 

 like moss that they have long been called moss animals or 

 Bryozoa. Some species live in colonies growing plant-like in 

 beds (PL VII) made up of hundreds or thousands of in- 

 dividuals (zooids) and to the naked eye they appear like deli- 

 cate stiffened threads; in others these animals are covered 

 with a limy crust, and in a few others like Pectinatella (Fig. 

 107) they are embedded in the surface of solid masses of jelly. 

 In any case, what we see when we pull the colonies from the 

 water are only skeletons or some kind of protecting covers, 

 in which the animals themselves are entirely hidden. The 

 individual animals are minute and visible only with a hand- 

 lens. When undisturbed they constantly rotate their head- 

 like lophophores in the tops of their tubes, or stretch them 

 from pores in the surrounding jelly; but at" the slightest jar 

 they snap them down, leaving no sign of life behind them. 

 But if a colony or even a fragment of one is allowed to rest 

 quietly in a dish of water for a few minutes, heads will all 

 rear up again, swinging and nodding back and forth as before. 

 The mouth of each animal is in the center of a circular or 

 horseshoe-shaped wreath of tentacles, this whole "head" 

 region being called the lophophore (Fig. 103). Each tentacle 

 is covered with cilia which wave toward the mouth, whirling 

 along whatever particles get into the current. 



131 



