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Bryozoans, also known as ectoprocts, are a family of small filter feeding invertebrates that live as colonies in aquatic habitats.  Of the several thousand species of bryozoans, almost all live in marine environments.  A set of exceptions are the 19 species in class Phylactolaemata which are found exclusively in freshwater lakes and resevoirs (Ruppert et al 2004). Pectinatella magnifica, the magnificent bryozoan, is one of these unusual freshwater bryozoan species, conspicuous in that it forms the largest colonies of the fresh water bryozoans (Wilcox 1906).

While most bryozoan colonies form as an encrusting layer on algae, pilings, or other submerged surfaces, a Pectinatella magnifica colony lives on the surface of a gelatinous mass.  When starting a colony, an individual animal (called a zoid) hatches from a hard seedlike "statoblast" and buds to form a small number of identical individuals.  This founding clump of zoids secrete a watery fluid that hardens to form a firm gelatinous core upon which the colony spreads as the zoids reproduce (first asexually and then sexually as the colony ages ) into visible rosettes of 10-18 individuals across the surface.  Before the gelatinous skeleton of a young colony hardens, colonies may fuse their masses together and form mosaic colonies from more than one genotype (Henchman and Davenport 1913).  An early study found that young colonies can propel themselves across the slippery surface of their gelatinous substrate by creating water currents with coordinated beating of the ciliated tentacles on their crown-shaped lophophore organ, a specialized filter feeding apparatus common to all bryozoans (Wilcox, 1906; Davenport 1899).  Pectinatella magnifica colonies can grow large, more than two feet (60 cm) across, and are found as a somewhat slimy translucent brown mass usually attached to an underwater substrate but sometimes free floating (Van Der Waaij 2009; Wikipedia 2013). 

The magnificent bryozoan is native to North America, originally to calm, preferably shady lakes and resevoirs east of the Mississippi.  It has, however, been introduced into Europe, Asia and Canada, and within the last 30 years it has become established in freshwater systems in the western US, in Texas, Oregon, Idaho and Washington (Wood 2010; Cannister 2013; Neck and Fullington 1983).  There is some concern that this species is becoming more common in areas outside its range, for reasons yet unknown (Virginia Institute of Marine Science 2010).

While P. magnifica does not impose great impact on humans, large masses of magnificent bryozoans can clog drains and waterpipes, and when washed up on land have a fishy smell.  Because the individual zoids remove particles from the water, the immediate result of their greater occurrence in non-native waters is to increase water quality.  A longer term effect, however, is that clearer waters may promote increase of algae which subsequently have access to more better conditions for photosynthesizing.  This may restructure natural ecosystems throughout a body of water. 

Link to the EOL Bryozoa page for more information about general biology of bryozoans.


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