You don’t need to put on your tuxedo or ball gown to order a seafood platter at Downtown, but you might want to consider it. After all, you’ll look like a million bucks when that blue glass bowl filled with crushed ice and tangles of seaweed is placed on your table, raised up on a stand for all nearby diners and passersby to see. Relax, though, it’s only $29. Not bad for three oysters and three clams on the half shell, three poached shrimp, a couple of crab legs, a lobster tail, and a small plate of salmon tartare, all with accompanying sauces such as a habañero and cucumber gelée. Richard Mazzera, owner, recommends splitting a half-bottle of Billecart-Salmon Brut Reserve Champagne ($32) with the platter; if you’d care for a more erudite bottle of wine, well, the sky’s the limit.