It is a real task to assign the proper name to each specimen that I encounter. Rotifers are extremely varied and I can never get the size of the specimen to match what the books indicate. The following image is a good example of this problem. The zooids were a good 500 microns in length and I can find no listing for the Peritricha being that large. Try a 'sky' filter that is used on cameras to protect the main lens.
Used ones are very cheap.
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