Wow, never realized they were that small.Here's a pic of mine. Yours is better. That's a bic pen for ref:
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Those are what I know as hydroids.The hydroids I had(have?) were like little tubes all over rocks, not the vermedit snails, they were in very dense cluster almost like carpet, somewhat soft to the touch. But damnit if they don't spread. Worse of all, whenever I'd rub up against them it'd get very itchy with little bumps.
Mine went away after a week or two too.Well it looks as though our little fellas disappeared.