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Archive for September 25th, 2013

beaverdamlake

As we lingered on the shore of Beaver Dam Lake, encountered on the Marble Rock Trail, we noticed strange, alien shapes in the water. They looked a bit like big masses of eggs, but autumn isn’t egg season.

The largest of the blobs was about a foot long or more. The masses seemed to be anchored to branches or debris in the water. A closer look shows that the mass surface was divided into segments with star-like white markings discernable.

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That evening, I sought out more information about the blobs. Dr. Fred Schueler of Pinicola kindly came to my aid and quickly identified the mystery mass as Pectinatella magnifica, a freshwater bryozoan. Please visit Pinicola.ca for a wonderful photo of a Pectinatella magnifica mass out of the water, glowing like Einstein’s brain with the sun shining through it (Page 17). It is part of a very useful guide ot freshwater species. About Pectinatella magnifica, this information is offered:

Our conspicupous Bryozoan is the vast jelly colonies of Pectinatella magnifica, filter-feeding colonies, up to two metres in diameter, that disintegrate into floating dot-like statocysts to pass the winter, and germinate into new colonies in the spring. Colonies are always composed of clearly recognizable rosettes of zooids on the surface of the jelly mass. In the water the surface appears white
from the zooids’ lophophores, and brownish when the lophophores collapse when the colony is lifted out of the water. As water temperatures fall below 20°C in the fall the zooids form into statoblasts which are saddle shaped with a single row of flattened barbed spines.

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The Encyclopedia of Life offers this information:

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).

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