The big red crustacean hunched over the Crawling Crab sign on Federal Boulevard lets you know that you’ll be swimming in uncomplicated seafood once you step through the door. And the rest of the decor echoes that promise: Life-sized sharks and pelicans swoop from the ceiling above life preservers, mooring ropes and raw timbers that seem salvaged from an old pier. Throughout the restaurant, the distinctive aroma of crab boil mingles with the sweetish, tidal notes of steam rising from boiling pots of crab, crawfish and shrimp. The Crawling Crab’s spicy Rajun Cajun sauce brings out the best in the boiled crawfish, while the more refined garlic-butter sauce offers just the right richness for meaty, whole blue crab. But this isn’t just a typical Louisiana seafood joint; it’s an example of the Vietnamese variation on crab shacks that began sweeping the country nearly a decade ago. Subtle Asian touches in the sauces and sides moor the restaurant more firmly in the here-and-now of the cultural collisions so prevalent on this stretch of Federal.