These pancakes are modeled after the popular Korean dish haemul jeon. The temptation to load these pancakes with every available shellfish at the fish counter can be overwhelming, but I recommend self-restraint; two to three varieties of shellfish are the most that should go into these pancakes. Generally I like to pair shellfish that have different textures; a favorite combination in my kitchen is shrimp and mussel.
When prepping the seafood, make sure that each piece is small enough that it doesn't overwhelm the pancake, but large enough that it does not disappear into the batter. Mussels will not need to be sliced, but will need to be steamed open. Oysters should only be sliced if they large. Shrimp work nicely if cut lengthwise through the middle (so that each half runs the entire side of the shrimp). Small bay scallops will not need to be sliced but larger scallops will; and finally, squid should be sliced as thinly as possible. Garnish with sliced scallions and lime wedges or an acidic dipping sauce.