I collected these same worms for a science project in jr high. They live in the stomach lining of a lot of ocean fish. Most notable are halibut and sandbass, along with a number of rockfish. We put them in fermeldahyde and they lived in it for several days!! These things are tough little buggers.

They can be very bad if eaten alive because they will burrow into your stomach lining, however cooking will kill them. There is a great section in the back of Milton Love's book "Probably More Than you Wanted to Know About the Fishes of the Pacific Coast" that tells all about them. What I do when I fillet a halibut is hold up the meat to the sun and look for the worms. They will be curled up in there and can be picked out with the knife. Yummy.