A "ticking time bomb" is a good comparison. They can be kept, but I suggest only in a species only tank, designed for this animal. They are filter feeders, and often tend to starve in some tanks. But you don't want any fish or critter that might pick at it...this can cause major trouble. The toxin they release is a fish toxin that will kill basically all of your fish should anything happen. They can be kept, but I recommend that it a lot of research is done into setting up a system just for them.