Biosphere reserves are significant means for the conservation of habitats and biodiversity, but require detailed knowledge of their fauna and flora to develop effective management plans. This study reports the known occurrence of 117 species of heterobranch mollusks (including 8 unnamed species) within La Reserva de la Biósfera Bahía de los Ángeles y Canales de Ballenas y Salsipuedes. The new genus Trivettea Bertsch is named. Range extensions and/or first records to and within Bahía de los Ángeles are given for 23 species. Triopha catalinae, Jorunna osae, Jorunna tempisquensis, Tritonia sp., Eubranchus madapamensis, Facelina sp. and Cuthona hamanni are reported for the first time from the Gulf of California.