I've read in some places they are just a type of aiptasia or others that they are curlicues. Either way, they seem to grow similarly and sting just as bad - I just used aip-x to eradicate them.
Its a goner. I Xed it and it had the wierdest implosion ive seen. It looked like it tried to spit it out by thrusting forward several times then bam it sucked in its hole never to be seen again.