Rinse and drain the cooled cuttlefish inside and outside. Bring half a liter of water, the juice of one lemon, vinegar, spices and half of the salt to a boil and cook the squid in it at a moderate temperature for about 20 minutes. Cool in the broth.
Put the mussels in a suitable bowl and stand covered with cold water for 15 min. Place in a colander to drain. Discard any mussels that have opened. Rinse the other mussels a few more times in fresh, cold water until no sand settles to the bottom of the bowl. Bring white wine to a boil with the bay spice, steam the mussels in it over medium heat in a covered saucepan for 5 to 10 minutes until they have opened. Transfer the mussels to a colander, discarding any shells that are still closed. Remove the meat from the opened mussels.
Rinse the shrimp after they have cooled. Boil half a liter of water with a quarter of the salt and the remaining juice of one lemon and cook the shrimp in it for 5 minutes (pre-cooked shrimp only for 2 minutes), drain and cool. Score the shrimp shell along the back with a sharp kitchen knife and remove the black intestines, detach the head with a slight twist, open the shell and remove the shrimp meat.
Remove squid from broth and cut into pieces, place in a suitable bowl with mussels and shrimp. Rinse celery and cut into small slices. Remove the peel from the onion