128 MOLLUSCOIDEA 



Occasionally one finds the fresh-water Bryozoa Fredericella and 

 Plumatella encrusting masses of vegetation and plant life in " pipe 

 moss." They die speedily when water is filtered, or when ground 

 water is used. The compound bryozoan Pectinatella alarms some 

 pond owners as it increases rapidly, forming a jelly-like mass, some- 

 times six feet in diameter. (Figure 54.) Bryozoa are eaten by 

 sharks, the cunner (a teleost), and an aquatic mammal, the " black- 

 fish." 



References on Bryozoa 



Allman, G.J. 1856. Monograph of freshwater Polyzoa. Proc. Roy. 

 Soc. 



BossLER, R. S. The Bryozoa or Moss Animals. Smiths. Inst. Rep. no. 

 2633. 



O'Donoghue, C. H. and E. 1926. Second List of Bryozoa from Van- 

 couver Island Region. Cont. to Can. Biol., N.S., iii, pp. 47-132. 



OsBURN, R. C. 1912. The Bryozoa of the Woods Hole Region. Bull, 

 of the Bur. of Fish., vol. 30, doc. no. 760, pp. 205-266. 



Class 3, Phoronidea. — The Phoronidea resemble the Bryozoa 

 in some respects and are usually placed under the MoUuscoidea. 

 Phoronidea are sessile marine worms bearing tentacles and living in 

 chitinous sand-covered tubes. The body of Phoronis is cylindrical, 

 and unsegmented, containing a large body cavity, with mesenteries 

 dividing it into three chambers. There are two circulatory fluids, 

 a colorless one in the body cavity, and the red hemoglobin-zonx.2\mvi^ 

 blood of the closed circulatory system. Phoronis is hermaphroditic, 

 the larvae in their metamorphosis passing through a stage called the 

 Actinotrocha. A horseshoe-shaped nerve ring is located at the base 

 of the tentacles, with two ciliated sensory grooves anterior to it. 



