Looks like a penut ... pull it
Regardless, my rule is “when in doubt, throw it out”.
Are some mysterious hitchhikers beneficial? Sure. Best case scenario, you get a single small member of your clean up crew, or the equivalent to a $3 snail. Worst case scenario, it can wipe out your $300 bounce mushroom in a few days, destroy your colony of Zoas in a week, or become a permanent pest in your tank. You’re risking all this for the potential benefits of a $3 snail. The cost/benefit analysis leans heavily in favor of throwing out everything that you aren’t 100% sure is safe.