Wikipedia
Pleurobranchidae
The Pleurobranchidae are a taxonomic family of sea slugs, marine gastropod molluscs in the clade Pleurobranchomorpha. Species in the family Pleurobranchidae have a prominent mantle and an internal shell that becomes reduced or is lost completely in adults. Some adult species have been seen feeding on ascidians. Larval pleurobranchids can be planktotrophic (feeding on plankton), lecithotrophic (deriving nutrition from yolk), or direct developing.
Many species produce secretions from their rich glandular mantle as a chemical defense against predators. Even the production of sulfuric acid has been reported.