Sounds like Daphnia, a crustacean, sometimes called water fleas, totally harmless and even tasty treat for some critters.
The jerky movement and if they are ďkidneyĒ shaped, they are Daphnia.
Your description sounds almost like Daphnia hyaline, an open water, high oxygen species.
If your Guru tells you otherwise and you are true believer that is okay I will not argue the point.
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I pretty much limit what I say to things that anyone can easily verify from recognized references or by direct observation. If it is my opinion I say so.
Last edited by Darkblade48; 12-18-2014 at 10:15 AM.
Reason: Please use the edit function for back to back posts to keep threads cleaner