Not sure what they are. I have the exact same thing. The wife and kids are calling them ( excuse the language) penis plants.......lol
Will follow this thread so I can find out as well.
Mine seem to inflate up during the day and then deflate at night.
I do have the same question out on reefsanctuary.com as well. Will let you know if I get a result.
They seem to be growing on the two pieces of rubble that I got from IPU, so they would have a Vanatu origin then. I believe that my puffer bit/ate one of them and I didn't notice any signs of ill effect, nor have any more been nibbled on ....
And they are also brackish tolerant with mine being at 16/18 sg.