I saw what I believe are detritus worms chilling in my tank, no major worry. But I also saw more of a short flat guy crawling along. I was worried it was planaria but for the life of me I couldn't see a trademark planaria head on it. It also bumped into a little bladder snail and recoiled in horror. After doing some searching it seems to look like a rhabdocoela, which are apparently not harmful? I couldn't get a very good pic but it looked like a semi translucent grain of rice, with like 3 or 4 white dots inside it. I couldn't notice a head or eyes.