What sort of parasite lives in my fish tank?

I have got a couple of yabbies in my tank along with a piece of driftwood I got from the same river about 4 months. Lately I am noticing a lot of snails in the tank and now have noticed a squid looking animal in the tank. Its very small and yellow and moves around by grabbing things with the tentacles. Im a little worried about my yabbies. Does anyone think this could be dangerous for the yabbies?