Much more lethal than a nem I think. I read they can die and decay very quickly, and are much more poisonous. They are beautiful though, and I like to have one some day. Tagging along.
I bought one couple of month ago. I think they are very inteligent and adapt quicker than any corals or nems. I even managed to target feed mine without it freaking out.
But let me tell you something., my brother's tank crashed and all his corals and fish died one after another. Water prams were all spot on. I suspect his sea apple died and poisoned his whole tank, again its just a guess. Im keeping a close eye on this one, the first sign of decay and its out. If I manage to keep this one for 6 month i will be getting a yellow sea cucumber too.
Never kept one. But a good friend of my at the aquatic critter Nashville, said for me to stay away from em. Just a tank crash waiting to happen, he said.... They are neat though.
Edit****
Anytime, I have a question about this kind of stuff, I hit up Advanced Aquarist and dig through their archives....
Might want to read through this it is alittle old, but still real vent I think.
I've had a Sea Apple for about 6 months and I find the care and upkeep to be relatively easy to handle. The most nerve racking thing about the Sea Apple is my wife knowing that it is poisonous and the shrieks that come from the living room each time the guy makes a move that she hasn't seen before. Recently I changed my aquascape and my apple was attached to the back of one of my towers that I was replacing. He wasn't budging, so I didn't want to stress him in tank and chose to do it out of tank to protect the other animals in the event of a worse case scenario. Luckily the apple was returned and finally in a spot where I can see him, but he's not causing issues. For my next build, the apple will likely go to the LFS when I am moving everything. As I travel a lot, I just can't handle a 100 percent tank crash in my absence (or presence for that matter).
Positives/Tips:
Easy to take care of filter feeders.
Could use some spot feeding, but be careful with spot feeders as they tend to cause the the apple to retract.
Great color addition to the aquarium
It looks like a baboon's bum.
Negatives:
They're like sea anemones, they go where they **** well please.
Mine had the habit of attaching to the glass so I couldn't scrape the glass underneath it.
It's not of matter of if, but when there will be a problem.