Tomalley, crab fat, or lobster paste is a soft yellow or green tissue found in the body cavity of lobsters and crabs. It performs the same function as the liver and pancreas in mammals. It is considered a delicacy, and is often used to thicken and flavor sauces. However, because the tomalley concentrates toxins in the marine environment, consumers have been advised to not eat tomalley in many regions of the world, including much of the Northeast United States.
Word origins
Carib tumale, "sauce of lobster liver"