BRYOZOANS 



water bryozoans have a multitude of relatives in the sea 

 whence they originally came. Their ancestors slowly mi- 

 grated up the brooks and rivers, or were carried inland by 

 animals, encountering ups and downs of temperature and 

 droughts which they had never met in the ocean. Nearly all 

 fresh water bryozoans have drought- and cold-resistant 

 buds, the statoblasts, each capable of forming a new colony. 

 They are groups of cells which form within the body 

 of an individual bryozoan and are finally set free in the 

 water after the animal has died and its hard outer covering 

 has broken into pieces. Often this does not occur until late 

 winter, although earlier in the year the current may wash 

 away everything which remains of a colony, statoblasts and 

 all. Some statoblasts are enclosed in tough cushions which 

 buoy them up like life-preservers, and armed with hooks 

 which anchor them to twigs and trash (Fig. 107). Thus 

 armed they are carried hither and yon by water and animals, 

 especially by water birds which transport them over long 

 distances into new regions. They usually hatch out in the 

 spring; that they are important safeguards against drought 

 as well as cold is suggested by the fact that some Brazilian 

 bryozoans form statoblasts although they have no winter to 

 endure. They achieve other ends, such as distribution, quite 

 as important to the animal as protection against cold. 



Habitat. — Bryozoans live in all kinds of fresh water, in 

 stagnant pools, ponds, and rushing streams. They form 

 delicate traceries on the undersides of flattened stones 

 (PI. VII), or grow vine-like on logs and boards which have 

 long lain in the water. Furry colonies of Cristatella (Fig. 

 108) grow beneath lily pads in quiet coves, masses of Pecti- 

 natella (Fig. 107) hang from submerged twigs. The latter 

 and other bryozoans are common in reservoirs. 



Food. — They feed upon microscopic organisms, chiefly dia- 

 toms (PI. IV). 



Aquarium study and collecting. — Quiet water bryozoans will 



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