I was on one of my gastronomic adventures and was in the middle of an island hopping trip when this was served in front of me in a floating restaurant - yes, it was floating and the only establishment in the middle of the salty sea! I was told that this is a rare water specie cooked in "kilinaw" cebuano style or in vinegar with onion and garlic. It has been 2 years since I first and last ate this and until now, I still can't figure out what it is. It tastes rubbery like squid or octopus and the vinegar made it really tasty served in its own shell - looks too big for an oyster or clam. Can anyone tell me what this is?