There are others, Ive only seen 2-3 at any given time. But yes, they haven't grown very large yet which surprised me too. I took 2 out total, but then just decided to leave any others I saw in until I was better able to ID them. The interesting part is that this tank has only ever had in-vitro plants with new filter media and new substrate. All of the equipment was bought new for this setup, and the fish I have in the tank were all quarantined prior to being introduced, then took a clean water dip right before being netted into it. I recently had a bout with seed shrimp in this same tank which I since have gotten to level out, and now these guys. They must have been some ninja hitchhikers. For a while, I was going crazy thinking they somehow came through my tap water, but now I'm just going with the flow.