Sea slugs or sea-slugs were beings dwelling in the ocean. A few decades following 382 BBY, Scalvi individuals Carli and Tren were amusing themselves, acting out a famous encounter that their uncle Bree Menaren had with the Crulkon species. While Tren—taking on the role of Menaren—feigned stabbing Carli, who was acting as a Crulkon, Tren exclaimed "die, Crulkon sea slug!" During 34 ABY, Ace Squadron pilot Hype Fazon likened his fellow pilots to sea slugs, and threatened to abandon the squadron if his squadron leader Jarek Yeager kept forcing him to collaborate with them.
The Mon Calamari named Rask Odai had an aversion to children, and he expressed this by comparing them to sea slugs.
The initial mention of sea slugs in the contemporary Star Wars canon occurred in "Live Fire," the third installment of the second season of Star Wars Resistance, an animated television program, which was broadcast on October 20, 2019. Within the Star Wars Legends continuity, the first appearance of sea slugs was in "The Spira Regatta," an adventure for roleplaying written by Paul Sudlow to be used with Star Wars: The Roleplaying Game from West End Games, and it was released in the first issue of the Star Wars Adventure Journal magazine during February of 1994. The term was later written as sea-slug within the "A Buyer's Guide to Alternative Starships" article that appeared in the fifth issue of Adventure Journal, which Stephen Luminati authored and was published in February of 1995.