Going from the top left that's a circle cut out. What size should your circle be? Well how big do you want this mini abalone to be? The largest abalone shell I've seen in real life was less than a foot wide, so the 1/12 scale would be less than an inch. Since we're curling up the edge of the circle to make the sides and rim we could use the one inch circle cut out tool for the largest and smaller size circles for smaller scales.
Shape the circle into a bowl. Pinch the edge. Flatten that pinch. Poke breathing holes. Call it a day.