The Kwakiutl (Kwakwaka'wakw) are reported to have eaten sea slugs in winter. If this report involves true sea slugs (rather than sea cucumbers, which are sometimes referred to as sea slugs), the species may have been the giant orange nudibranch. Kwakiutl were reported to collect them when the day was calm and there was a low tide. A canoe was used to travel to regions where sea slugs were known to be on the ocean floor and a special shaft with a few short wooden prongs attached at the end was used to pull them up into the canoe. The head was cut off and the insides squeezed. When the canoe was full, he returned to the shore where his wife would squeeze out the insides from tip to end a second time and place them in a basket. The slugs were soaked in clean water for two nights. The water was again squeezed out, and they were added to boiling water along with hemlock branches and handfuls of dirt from the floor of the house. The dirt was said to prevent the kettle of sea slugs from boiling over. They were sufficiently cooked when they could be pinched with a tong without slipping away. They could also be roasted in a fire while turning them often. Once the sea slug was stiff it was put into fresh water and the ashes were scraped off. Sea slugs could also be baked by digging a hole in the ashes of a fire, laying them in the hole and covering for thirty minutes. As the slugs were prepared they were given to the guests until they were satisfied, the remainder were then given to the women .
Boas F: Ethnology of The Kwakiutl-Based on Data Collected By George Hunt (Part I), vol. Smithsonian Institution Bureau of American Ethnology. Thirty-Fifth Annual Report. Washington, D.C.: Government Printing Office; 1921
Sea slugs, like sea snails, all belong to a large group, called gastropods, including over 50,000 species of snail and slugs. In North America, sea slugs include one nudibranch species, the giant orange nudibranch (Tochuina tetraquetra), occurring along the Pacific coast from Alaska to California. They have no external shell, are known for their striking colours and their external gills, and are considered the largest species of nudibranch, attaining up to 30 cm and 1.4 kg.
Howes GJ, Chatfield JE: "Mollusks". In: The Encyclopedia of Underwater Life. Edited by Dawes ACJ: Oxford University Press; 2007.