You need to learn to dissect the ostracod to obtain the appendages and array them individually on a slide for examination. You also need unbroken valves to see the correct shape. Pay attention to internal features: marginal areas, the hinge structure and the muscle scars. These will get you started with the high level taxonomy, but I think that it will need to be by examination of the appendages that you will get closer to species level. 

You need to take dimensions, so it better to put a scale bar.