Wash and destem mushrooms; discard only about half of the stems, save the balance. Take crab, all but 10 shrimp, the cilantro, green onions, water chestnuts, and the stems you saved and chop up fine in a blender. When done place in bowl; fold in breadcrumbs. Melt butter in another bowl; dip each mushroom cap completely into butter and fill generously with mixture from bowl. Place stuffed mushrooms on small muffin tins; do not shove in, place on top. Place in oven at 350 degrees for 15 minutes. Take from oven let cool slightly; reset oven to broil. Get the remaining 10 Shrimp and slice in half lengthwise. Place on top of each filled mushroom and broil for a few minutes or until a slight crust forms on top.