Yep.it's an ascidian. Anyway..marine snow is actually processed and by rights, dead. So if you overdose there is a slight chance of an ammonia spike. For DT it is not so serious as it is said to be in suspended animation, resulting from lower temperatures. So when you add it into your tank it becomes supposedly live again. They can survive in your water longer and it will take a longer time for an overdose to result in an ammonia spike.