“Try this,” Mark Marhefka said, peeling shell off a bright pink but undeniably raw shrimp. The first bite — tender and sweet — was heavenly. They're Royal Reds, a little-known variety found in the deep water way off the Atlantic Coast. More delicate than white or brown shrimp, they don't travel well and scientists don't even know that much about them. Marhefka buys his from a Florida connection and, while they last, resells them at his Abundant Seafood stand on Shem Creek. If you luck into finding them, buy as many pounds as you can afford.