Put clams and mussels in big bowls covered with salted cold water.
Let them rest for few hours.
In a large, short pan (if earthware is perfection) sautee oil with minced onion and garlic.
Add chopped squid, cook with a lid on medium fire for 15 minutes.
Add vinegar, let it evaporate for a couple of minutes then add tomato sauce; bring it to a boil then add monktail, redfish, cook for ten minutes and add mantis shrimps and all the seafood except clams and mussels.
Cook with a lid on on gentle fire for about 40 minutes, add some water if it gets too thick.
Almost at the end add clams and mussels and parsley, mix well, cover with a lid until they open.
Adjust salt and pepper ( I use a sprinkle of chili flakes) and serve with thick bread slices, toasted.