More likely what has happened is that they have reached the point they were no longer able to stay together. Literally they fell apart.
Most of the 'nepthias are non photosynthetic and require massive feedings which no one as I have seen yet are able to provide in a tank to keep these corals alive. Even then it is a guess that it is massive feedings that these corals require for survival.
Basically your coral starved and disintegrated I am betting. These corals do not belong in our tanks at this time. We don't know the requirements to keep them and all that ends up happening is that they starve and die.
hth
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Darren
Always strive for the optimum environment, not the minimum environment
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