Disappearing Fish -- Please Help

[lark]

90 gallon, 110 lbs live rock. Before fish started disappearing, the inhabitants were: 3 small green chromis, 1 Royal Gramma, 2 Peppermint Shrimp, 1 small cleaner shrimp, 1 small (2") filamented wrasse, 1 brownish (definitely not green) brittle star (about 8"), 1 small finger leather, daisy mat polyps, a few mushrooms, and a very small colony of zoanthids. Astrea snails and some hermits.

The corals and mushrooms are doing great. I test frequently, and everything is great. Acrylic tank with openings, covered with egg crate (and no evidence on the floor of jumping).

Over the course of the last three weeks, I've lost 4 animals. First to go was the cleaner shrimp. He just disappeared. No sign of him. (At first I thought I found him, but it was just the remains of a molting from one of the peppermints.) Second was the wrasse. Third was one of the chromis, and now another yesterday.

Brittle star seems to me to be the most likely culprit, although I through the green ones were the ones to stay away from. But since I bought him I virtually never see him. Sometimes, I see a leg sticking out from under a rock. Could he really catch, kill, and eat 4 animals in 2-3 weeks? I put little morsels out for him, but rarely see him (although they are gone in the morning.) I guess I could understand if something else in the tank was killing them, and he was cleaning up, but how does he catch them? (Ok, the wrasse would have been easy.) Could a mantis shrimp do this? I purchased the zoanthids not too long ago, and the disappearances started thereafter. They came with a nice piece of live rock -- about 6 inches square. Could something nasty have been in the rock? How do I find it?

Obviously, I need to get the star out of the tank and see if it improves the situation. Catching it is going to be a bear. If anyone has any suggestions, or if anything I've described makes it unlikely to be the star, please let me know. Very frustrated. I really liked that little wrasse.

Oh -- one other piece of the puzzle. My peppermint shrimps' tails are turning blackish, but they otherwise seem to be doing fine. Is this natural? Could it be a clue?

[plummike]

Could be a crab that hitchiked in your rocks and is growing. Try looking around in the rocks white a flash light after lights out. If you put red celophane over the light it won't startle the crab into hiding.