PIPE MOSS 



Bryozoa 



The freshwater Bryozoa, or "pipe moss," are a group of 

 invertebrate aquatic animals that are often mistaken for a mat of dead 

 moss. Colonies of these animals are plantlike in appearance except for 

 their coloration, which is brownish-white. Bryozoa attach to logs, 

 rocks, and other submerged objects, usually where the light is relatively 

 dim. They have been found on a number of irrigation systems growing 

 in profusion on concrete canal linings, submerged inlet screens, 

 louvers, trashracks, and on the inside of pipes (insert 1). The individual 

 animal is microscopic, more or less cylindrical with a thin body wall. 

 These animals secrete a thin protective layer about the body wall. 

 Many of the individual animals grow in close association with one 

 another to produce a connected, highly branched, antler-like colony 

 (insert 2). The protective coatings of these colonies of animals are the 

 most conspicuous feature, being massive and tough, or delicate and 

 gelatinous, depending on the species. Oftentimes, young colonies 

 continue to grow on the remaining protective layers of the dead 

 animals, thus producing a thick mat on a solid substrate. 



The individual animals feed on various microscopic plants and 

 animals that are swept into the animal's digestive system by a crown 

 of tentacles. Tlie tentacles when extended have the appearance of tiny 

 delicate flowers (insert 3A). A slight disturbance in the proximity of 

 the animal will cause it to retract the tentacles in a flash. Most 

 bryozoan colonies are stationary, but a few species are capable of 

 sluggish movements. The colony can grow asexually where a portion 

 of the body wall grows outward to produce a new animal. 



A unique feature of the Bryozoa is their ability to produce a highly 

 resistant body called a statoblast or sessoblast (insert 3B). This seedlike 

 body develops from asexual budding. This structure provides for the 

 species to be carried over during unfavorable environmental conditions 

 and for geographical disseminations. 



Bryozoa growing on submerged water structures and in conduits 

 have been known to create serious hydraulic problems for water 

 distribution structures. Two bryozoan species known to infest Water 

 and Power Resources Service irrigation systems sufficiently to become 

 problems are Plumatella repensL. and Fredericella sultana 

 Blumenback. The latter species is illustrated. 



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