Season sea bass, shrimp, and scallops with salt and pepper; set aside.
Heat oil in Dutch oven over medium-high heat until shimmering.
Add mussels, basil, sherry, garlic, Worcestershire, saffron, and ½ teaspoon salt.
Cover and cook until mussels start to open, about 2 minutes.
Stir in clam juice and marinara until combined.
Nestle sea bass and scallops into pot and bring to boil.
Reduce heat to medium, cover, and simmer until seafood is just turning opaque, about 2 minutes.
Nestle shrimp into pot and return to simmer.
Cover and cook until all seafood is opaque, about 3 minutes.
Remove from heat and let sit, covered, for 5 minutes.
Serve with baguette slices and lemon wedges.