The two species sold in the "trade" are Pseudocolochirus violaceaus (Indonesia) and Pseudocolochirus axiologus (Australian), both being quite sensitive and not recommended for even the most experienced hobbiest.
Personally I would highly recommend against anyone keeping them or at the very least in fishless systems. Not only for the reasons mentioned above about their death throws but also if you happen to get a female. I had the Indo variety and kept it quite happily for several years. Unfortunately too happy, it eventually spawned releasing it's eggs into the tank. It was shortly after lights out and I would never have known except I noticed a fish float by (note not swim by). Upon closer inspection, several fish where "floating" by. Turned on the lights only to witness all the fish either dead or dieing and the sea apple happily spawning eggs. I removed the sea apple immediately and siphoned any/all eggs found to no avail. The eggs are extremely toxic and the impellers in the exuipment ever so helpful in releasing those toxins. Fortunately fish was all that was lost but sad just the same.
Cheers
Steve
