That looks like a spiral snap ring but I have not seen one in any of the Mopar transmissions I have done. I have seen them in brand X.
Here is a good site to see the exploded view of the a500. I don't see any spiral snap rings in the picture.
[URL]https://www.transpartsonline.c...t.php?TransPartsOnline=500&TransPartsType=500[/URL]
FYI many rebuild kits have extra parts because the kit is used for multiple years of transmissions.