The other 3 large ones looked exactly like the small bulb nem when they were younger.
Bulb nems are currently unclassified, but work is being done with them and they are getting more attention in regard to classification.
In that work, it has shown that they do behave very similar to e. quadricolor (bubble tip nems). Some will show the bulbs and others will get stringy. Due to so many variables (like with BTA) it is not really sure why some "Bulb" and some do not. In addition, you can clearly see that these are not typical aiptasia. The way they are situated around the disk is the give away and hard to explain.
I will say, these nems may end up being classified in the family Aiptasiidae (they do have a few characteristics shared with them, but have quite a few they do not), but who knows when or if that will actually happen. Heck they may even be grouped with the Bunodosoma family since they do not rapidly reproduce or make multiple babies when moving or are shredded. I would prefer the latter be used if they do just want to lump them into an existing family. But again, who knows. Nems are not really at the top of the "studies list" for organisms from the US coasts. It is all about the elk horns, stags and other hard corals for the time being.
Biggest thing is to treat them like any bubble tip nem for the time being. They can existing a reef tank, but you have to accept they may walk all over things like BTA do if they want to move spots. The area thing is that (at least the ones I have and the ones I have seen kept and not killed) do not spread rapidly like aips and tend to stay put exactly where they were when noticed.
Edit: Forgot the fish part.
As with any anemone, they do stand a chance of catching a fish if it swims into them. The great thing is that they are not active hunters, a healthy fish should not have an issue avoiding them, and their not as potent of a sting or as sticky as a haddoni or other carpet nems. Plus, most fish know to avoid them.
