An unusual tissue covering the tongue and occasionally part of the gill chamber of many species of the Indo-Pacific cardinalfish genus Siphamia is described and compared with an earlier description of a similar tissue found in the cichlid species Alcolapia grahami inhabiting lakes of the African Rift Valley. Species of both genera are mouth brooders. The Siphamia tissue is globular and its cells are oblong, whereas the A. grahami tissue is single-layered, with larger, columnar cells. The tissues of both have the characteristics of a mucosa and show evidence of active synthesis. While ion regulation has been proposed for the A. grahami tissue, the function of the Siphamia tissue is unknown, but a role in feeding, or antibiotic or appetite-suppressing functions have been suggested.