Yep, they are so cool that I am looking for ways to rid the tank of them. They started out as 1 or 2 on a heater, and now I must have 100+ in the tank. I made the mistake of scraping them off the heater while it was in the tank. The floated around the tank and attached themselves to the plants, the sponge filter, the canister filter intake, the tank walls, and the plants. Now, I have a mess in my tank. If I had known they were hydra, I would have taken the heater out and scrubbed it down in the sink with some soap and water. What a PITA this is going to be.