Humm. The plastic is 'threaded' from something that scored the impeller plastic and probably the impeller cavity. Looks to me like tiny rocks or perhaps course sand entered the pump and wore a hole through in the impeller plastic. I would carefully inspect the impeller cavity to see if it too is scored. Hopefully, you don't have a larger problem than just replacing the impeller.Go the impeller out. Looks like water got into it and rusted it, then it exploded.
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