Bring two large pots of water to a boil and add enough salt to make the water taste like the sea. In one of the pots, boil the the pasta according to the package directions.
Add the olive oil, parsley, cilantro, chervil, garlic, parmesan and salt to a small food processor and process until smooth.
In the other pot, boil the shrimp until just cooked. The exterior will turn pink when cooked, and the flesh will go from translucent to opaque. The time will depend on the size of your shrimp, but mine took about 1 minute. Drain and cover them with plastic wrap to keep them from drying out.
Quarter the avocado, and then remove the pit. If your avocado is ripe, the quarters should peel easily by hand. Slice each quarter into 1/8" thick pieces and drizzle with the juice of 1/4 lemon to keep them from turning brown.
When the pasta is done, drain it and add it to a bowl along with the shrimp, crab, avocado and pesto. Toss with tongs to coat everything evenly, then serve immediately with lemon wedges.