POLYZOA 
MONG the numerous objects to be found on the beach at 
low tide are the Polyzoa, of which there are said to be seven- 
teen hundred named species of the marine forms. These little 
animals, although so plentiful, are inconspicuous, and it may be 
said that their very existence is not known to those who are not 
professed naturalists; yet they are easy to see, incrusting with a 
delicate calcareous lacework the surface of stones and shells and 
seaweeds in the tide-pools, and hanging from the rocks like 
branches of delicate seaweeds. There is hardly a frond of even 
the fine red alge on which cannot be found the little tube holding 
shelly saucers, or the creeping stems or branches of polyzoans. 
Any one of these little masses, when examined with a pocket- 
glass, will surprise one with its delicate and beautiful structure. 
This class of animals is also called Bryozoa, and certain species 
have the common names of sea-mats and corallines. They are 
broadly divided into two groups, namely, the erect and the in- 
crusting forms. Those having tree- or plant-like shapes resemble 
seaweeds, while the colonies which spread over stones, shells, and 
algze resemble moss, hence the name Bryozoa (moss-animals). 
Both groups have the general appearance of hydroids, because, 
like them, they are colonies having plant forms and having 
their organisms inclosed in cup-like sheaths. The resemblance, 
however, is but a superficial one, for the Polyzoa have a much 
higher organization, each animal of the colony being a separate 
and distinct individual. They can easily be distinguished by the 
hair-like processes on the tentacles. The ciliated tentacles and 
complete alimentary system are the conspicuous differences be- 
tween these colonies and those of the hydroids. 
The Polyzoa are very numerous and form a most attractive 
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