I got a call from my friend today that said "dude, you're (Gigas) clam thats always open real wide is split in half, man. The snails are swarming it, and its open way bigger than before, did it explode?"
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As soon as I get over there, I notice it looks as if the area below the mantle in the front (lower than the opening exposing the gills) has separated. The shell has been split at the end, but the mantle is by no means ripped, it just looks hurt.
WTF is the cause (as he has NOTHING but a Yellow Watchman Goby, Green Chromis, some snails and crabs in the tank he's holding my inverts), because he said nothing was aggitating it until this happened. While it is true that the clam was generally more spread open than the rest of my clams, it never looked bad, or had adverse effects, til this.

I'll post a pic in a minute, to see if I can make the problem more clear.