Histological description of tooth formation in adult Eretmodus cf. cyanostictus (Teleostei, Cichlidae)

Summary etmodini, a tribe of closely related cichlids (Teleostei, Cichlidae) originating from Lake Tanganyika, possess oral tooth shapes ranging from conical (in Tanganicodus) over cylindrical (in Spathodus) to spatulate (in Eretmodus). Prior to a study aiming to understand how these distinctly different tooth shapes can be acquired in such closely related taxa, a detailed histological study was required of tooth formation in a representative of the eretmodines. Here, we present a histological description of replacement tooth development in Eretmodus cf. cyanostictus. Using light-microscopic observations on semithin as well as on ground sections, microradiographs and stereo-microscopic observations of both alizarine red S stained and unstained jaws we can conclude that tooth formation in adult E. cf. cyanostictus roughly corresponds with what is known for teleost tooth development in general. Remarkable features include the localization and shape of the epithelial downgrowth, the transient presence of a layer intermediate between inner dental epithelium (IDE) and outer dental epithelium (ODE), the asymmetric shape of the enamel organ, the fact that the pulp cavity recedes in front of the forming enameloid during enameloid formation, and finally, the pattern of matrix mineralisation and maturation, and the presence of pigment in the enameloid. The observation that the enamel organ in adult E. cf. cyanostictus develops asymmetrically is significant for understanding tooth shape variation in the Eretmodini.