Kill the geoduck by dunking it in boiling water for 10 seconds, and then plunging it into an ice bath.
Remove the shell and capture the juice.
Clean and dice the body meat in ½-inch (1-cm) pieces.
Peel the skin off the neck of the clam (I’ll just say it—it’s a little creepy, like removing saggy skin from a prosthesis) and dice the neck meat.
Toss body and neck meat with salt and shiro dashi to taste, and refrigerate for at least a few hours. (The body meat is fatty and a little gamy—in a good way—the neck meat clean and delicate. I like them together.) It should be assertively seasoned, still sweet but with a whisper of ocean.
To make the vinaigrette, combine all of the ingredients and season with salt. If the Meyer lemons aren’t sweet enough, add a pinch of sugar. It’s an alluring vinaigrette, the shiro dashi adding a bump of umami where you don’t expect it.
For the clam gel, sweat the shallot, garlic and piment d’Espelette in the olive oil until tender. Add the squid ink and cook for 2 minutes. Add the white wine and Manila clams, cover the pan, and steam until clams are opened. Cook 2 minutes more and strain the liquid through cheesecloth. Discard the clams, and cool the liquid in an ice bath. Season with Meyer lemon juice and the juice from the geoduck, which is salty, in place of salt.
Bring a 150 g of the clam juices to a boil with the agar, and then off the heat whisk in the gelatin to dissolve. Add to the rest of the clam juices and check the seasoning—it should taste dark, briny and bright, like clean coastal waters. Pour 218 g for a 12 x 18-inch (30 x 45-cm) sheet tray, and let cool in the refrigerator. Cut into 1 x 3-inch (2.5 x 7.5-cm) strips.
Cook the bull kelp in simmering unsalted water until just tender. Cool on a sheet tray lined with parchment, and cut also into 1 x 3-inch (2.5 x 7.5- cm) strips. Soak in several changes of water, drain and refrigerate.
To serve, toss 48 pieces of geoduck and 12 strips of bull kelp with Meyer lemon vinaigrette, salt and black pepper. Arrange in a bowl, interspersing with strips of clam gel. Garnish with tiny wild fennel shoots and Meyer lemon zest.