Published records of the azooxanthellate coral species Leptoseris troglodyta Hoeksema, 2012 are so far limited to the western Pacific (Hoeksema 2012, Waheed et al. 2015). Since 2018, through a citizen science program, members of the Deep Blue Exploration (DBE) association (www.deep-blue-exploration.com) based in Mayotte, southwestern Indian Ocean, have conducted methodical surveys of the morphology and biological components of the mesophotic environment on the deep fore reef slope of the barrier reef surrounding the island. During these surveys, a number of large submarine cavities and caves opening between 65 and 90 m depth have been explored using trimix rebreather tech diving. Despite the depth and the topography of the cavities, implying drastically reduced light conditions, their examination has revealed the presence of a rich cavernicolous (coelobiotic) benthic fauna.