Looks like a mini ramshorn. They are really flat like a disc and stay very small, like 2mm. I have them in most of my shrimp tanks and don't mind them at all. If you have a decent population of MTSs, the MTSs will outcompete them for food. Perfect dwarf puffer food.
20g L46/hastatus/pygmy corys, 10g OEBTs, 10g blue bees/blue velvet shrimp, 10g CRS, 25g L174s/BNs/L340s, 10g yellow/red tiger shrimp, 15g clown plecos/CPDs/habrosus corys, 15g cory fry, 29g Weitzmani/panda corys/BNs, 46g L134s/salt and pepper corys/BNs/rubberlip pleco, 55g SAE/L201s/L199s/BNs/kissing gourami, 75g L316s/BNs/L134s/CAE/silver dollar, 30g L340s/L211s/CPDs,10g tangerine tiger/snowball shrimp, 20g L134/habrosus corys, 10g CPD fry