Shipworms are not worms at all, but rather a group of unusual saltwater clams with very small shells, notorious for boring into (and eventually destroying) wooden structures that are immersed in sea water, such as piers, docks and wooden ships. Sometimes called "termites of the sea", they are marine bivalve molluscs (Eulamellibranchiata) in the family Teredinidae, also often known as Teredo Worms.
In Palawan and Aklan in the Philippines, the shipworm is called tamilok and is eaten as a delicacy there. It is prepared as kinilaw - that is, raw (cleaned) with vinegar or lime juice, chopped chili peppers and onions, very similar to ceviche. The taste of the flesh has been compared to a wide variety of foods, from milk to oysters. (and yes, it tastes just like oyster and you can have a lot of it!) (Credit to Evz Montz for this pic as we were eating our lunch)