Make the stock - place all the stock ingredients into a sauce pan, bring to a boil, lower heat and simmer for about 45 minutes. Shut off and allow to seep for 15 to 20 minutes. Remove all the vegetables with a slotted spoon.
Meanwhile, put the shrimp shells into a small sauce pan with 2 cups water, bring to a simmer and allow to cook for 30 minutes. Shut off the heat and let sit to seep for 15 - 20 minutes.
Strain the shrimp broth into the stock; bring to a simmer over medium heat.
Place the thinly sliced scallop into the bottom of a small soup bowl.
In a separate skillet, heat the wine and garlic together, add the mussels and cook, shaking the pan, until the mussels open. Discard any that do not open. Put the cooked mussels into the soup bowl.
Add the coconut milk and fish sauce to the stock; when just simmering add the shrimp; cook for 3 minutes, or until just cooked. Remove the shrimp to the bowls, distributing them evenly. Bring the stock to a simmer, taste and adjust. (If it doesn't seem spicy enough, then add a little Thai curry paste, green or red, you want some heat). Ladle the hot stock into the bowls (if the scallop is thinly sliced it will cook in the hot broth); top with a sprinkling of cilantro and green onions, serve the lime wedge on the side.