Here is what I found:
<span style="color: #333366">Why do some mantis shrimps' raptorial appendages "fall off"?</span> (Dr. R. Caldwell)
First, stomatopods have ways of dealing with this. If they are missing a single raptorial appendage (2cd maxilliped), there is no modification of the molt cycle and they molt at a normal rate. They usually have no problem feeding, although smashing shells may take a bit longer. If the entire appendage is lost, after one molt there will be a small, poorly colored appendage. It will not be functional. After a second molt, it will be a little more than half size and will move, but not strike very well. After a third molt, it will be 3/4 size and functional (but weaker). After a fourth molt, you won't know the difference. Given that it may be a couple of months or more between molts, it can take up to a year to regenerate the appendage. Juveniles can do it in a couple of months.
If both appendages are lost, the animal has to eat prey that it can chew - worms, soft meat, etc. However, it will put all of the energy it can into molting resorbing the ovaries or testes, etc. It will molt up to 50% faster and if it is fed well, can grow the appendages back to full size in about 2/3 the time it takes to grow back one. Obviously, however, this is at a cost. It does not reproduce and energy reserves are dangerously low.
As to why the animal lost both rapts, I would guess some sort of stress. Heat, cold, salinity, organic solvents, etc. can all cause the muscles in the raptorial appendages to be permanently damaged. The rapts don't fall off, the stomatopod literally breaks them off. Stomatopods can't autotomize its claw the way a lobster or crab does, so it grabs the appendage with the other maxillipeds and twists it back and forth until it breaks free.
The other common cause of rapt loss is during the molt, but often this involves just a single rapt. Also, loss during molting is not as common in Gonodactylids as it is in O. sycllarus. <p style="text-align:right">- Dr. Roy Caldwell
