Check out this Reef Sites article on the predation of sea slugs by corals, written by our team and published in Coral Reefs in March of 2015.
“Only a few documented examples are known of predation on sacoglossans, which are heterobranch sea slugs famous for ingesting the cellular contents of algae (Krug et al. 2013). Known predators of sacoglossans include, for example, species of fish and crabs (Trowbridge 1994). Information on scleractinian corals eating large-sized prey became only recently available (Hoeksema and Waheed 2012); therefore, it is not surprising that no examples have been reported on sea slugs being eaten by corals.
During a field survey on a fringing reef off Sai Tong beach (10°03′41″N, 99°49′30″E) on December 22, 2014, at the island Koh Tao (Gulf of Thailand), a sacoglossan gastropod, Plakobranchus sp., was found being consumed by a monostomatous mushroom coral, Pleuractis paumotensis (Stutchbury, 1833) for 20 min (1320–1340 hrs). The coral was part of a mushroom coral assemblage on a sandy substrate (9 m depth) that is rarely visited by divers.”