My partner just noticed then in the tank tonight, and a preliminary search hasn't yielded much help. It is in my refugium (hence the Caulerpa). I know it's not an Aptasia, but not sure what it is. It has a short stalk (less than half an inch tall), and has maybe 6-8, thread like tentacles probably almost an inch long. Any ideas on if this is something to have in the tank or something that could cause a problem if it got into my main tank, please let me know. Have a good night (or day depending on when you read this).