cercaria of Paragonimus westermani of the microcercous form with a rudimentary tail (button) seen to the extreme right.  This cercaria will emerge from its snail host, family Thieridae, and rather than swimming will "inch" along wet rocks, seeking its crab or crayfish host (11 different species).  There is the possibility that crabs and crayfish hosts may become infected by eating infected snails.  400x