This critter was in an established tank we got from someone else. When fully extended the trunk is about 3 in high and the tentacles are about 1-2 in long. It does not host the two black clownfish that are also in the tank. It periodically pulls all its tentacles in which someone told us means it is eating, but I don't know what unless it grabbed a piece of the mysis we sometimes feed to the clowns. I haven't seen it do that and the fish are pretty good at gobbling the mysis so even if it is getting some of that from time to time I don't think that is enough to sustain it. I've tried giving it small bits of raw shrimp which it grabs, pulls halfway into its mouth, then rejects. I'm concerned that it's dying because throughout the day it repeatedly shrivels down to half or a third of its full size, then gradually re-expands. A kid at LFS told my husband that we don't have to feed it, which I highly doubt! Any better ideas?