Bryozoans are much more common than I realized initially. Early in my poking about in pond water with a microscope I ran across bryozoan statoblasts but didn't have any clue what they were. I had a sample from a nearby pond in which I would find a shell on about every third try. This picture is one of the first I took when I finally got a digital camera. Sometimes there was more than one statoblast on a slide. Shortly, I happened upon a statoblast which was awakening and got nice a series of pictures:
Bulging out of its shell
Extending with the shells separated
Tentacles deployed for feeding, this took a couple of minutes and was very tentative
Another picture of the animal feeding by filtering water. Cilia on the tentacles produce a noticable flow; the tentacles move only slowly but can retract quickly. This series of pictures, taken over about 10 minutes time, I suspect is uncommon -- I haven't found anything similar on the net.
A statoblast with a neat racing stripe
Shell open so it is apparently hatching
Statoblasts in brightfield are not so eye-catching, darkfield is much prettier
A closeup showing the glittery mother-of-pearl look to the white area
I never did identify the statoblast myself. Finally, Prof. Howey from Wyoming identified my pictures as bryozoan statoblasts, probably plumatella. He suggested "Fresh-Water Invertabrates of the United States" by Robert Pennak as a reference; I purchased a copy and it is a VERY helpful reference. Unfortunately, I didn't get around to looking for a plumatella colony at the original pond until October -- I found a colony, looking as and where Pennak lead me to expect, but the animals had died from the cool temperature. However, there were numerous statoblasts embedded in the remains of the colony, making identification easy; this summer I should be able to find a live colony and get pictures.
In May 2003 (in my first sample from the same nearby pond) I found a statoblast which had begun growing and will eventually become a plumatella colony. Here are pictures in BF and DF:
The bryozoan, tentacles deployed, with the statoblast shell barely visible at the base.
The statoblast shell is in focus in this DF picture. 100u/#division
Plumatella are fairly common in ponds and streams which are shaded by trees, where the colonies often grow on submerged twigs and leaves. Plumatella colonies look more like moss than the animals which they are. Individual statoblasts are about 1/2mm long and glint in the sun; sometimes vast numbers are released and cause the water's edge to look silvery by their presence. A 10x magnifier will provide a better look and allow identification.
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