To give an idea of scale, it's a grain of sand... and beside it sets the organism in question.
Three of them.
Going by the "Aids to the Recognition of Fresh-Water Algae, Invertebrates and Fishes," a brief 24 page paper which my instructor photocopied for me to use... the closest, is Merismopedia. But, that may be wrong. This species could also be, "Crucigenia rectangularis," both look practically the same.
Needless to say there may be others that look similar or near identical.
I've surfed the web, and really ran into some problems with species identification -- for that matter, proper classification into genus.
This was written by a biology instructor, in regard to the trouble I've had identifying species writes:
The proper way [to collect plankton] is to use properly calibrated and sized plankton filters.
I recognize the eagerness which you show in searching out and trying to identify the enormous range of things you can find. It is what is found in the best students; those truly interested in learning as opposed to those who simply want to get through the required laboratory exercises and go home. Unfortunately, there are not simple answers to questions, even "simple" questions like "what is this". Especially not when the sample comes from teaching aquaria that may be filled with all sorts of exotic things. You are faced with more than the "common pond life" that the simple-minded keys I referred you to are intended to help with.
You are also learning the fact about photographs -- some of yours are unusually good but they simply do not convey the detail of information that a trained eye can see, especially as the trained brain integrates the information from different views and images from different angles. That is why making drawings is so important. In a good drawing, you illustrate those features that are really important, showing them clearly. Of course the Haeckel episode reminds us that drawings are different from real life, but photographs are also different from real life. Making truly detailed and useful photomicrographs is a talent that requires special training and long practice, not to mention rather better microscopes than what you are using. In other words, there really isn't enough detail in the pictures you display to see exactly what many of the things may be. Your commentator on the artscape salt-water-microbes web site identifies things as well as can be expected.
I hate to have to tell you this, but you will have to accept that some things will not be identifiable. That will come with long experience studying with experts. The fact that one of your instructors/mentors, Terri, apparently can't identify it all should be a clue. That is why doing science is a constant learning experience. It really does take years of guided training to do some things and, even then, you still keep learning as long as you live.
So welcome to the world of real science! You are off to an excellent start. You have a long way to go but the entire trip is a fantastic adventure!
- R. Norman