FONTANA, M. F.; ASK, K. A.; MACDONALD, R. J.; CARNES, A. M.; STAUB *, N. L.; Gonzaga University, Spokane, WA; Gonzaga University, Spokane, WA; Gonzaga University, Spokane, WA; Gonzaga University, Spokane, WA; Gonzaga University, Spokane, WA: Loss of traditional mucous glands in the plethodontid salamander Ensatina eschscholtzii

Amphibians possess two types of skin glands: mucous glands and granular (serous) glands. The presence of these glands is used to define the clade Lissamphibia. Mucous and granular glands have evolved independently and have distinct morphologies and secretions. Mucous glands are typically small, widely distributed on the body, and produce an agranular, fibrous or flocculent secretion that stains positively with the periodic acid-Schiff reaction (PAS) (indicating neutral carbohydrates), positively with Alcian blue and metachromatically with toluidine blue (indicating acidic mucosubstances). Granular glands are larger than mucous glands and secrete a proteinaceous granular product. We use a variety of histochemical tests to identify traditional mucous glands and mucus in the plethodontid salamander Ensatina eschscholtzii. Acidic mucopolysaccharides and traditional mucous glands appear to be absent: gland cells and their secretory products are negative for Alcian blue, orthochromatic for toluidine blue, and no glands produce an exclusively fibrous secretory product. Instead, Ensatina produces neutral mucus in specialized granular glands. We name these glands mucus-producing granular glands (MPGGs). The MPGG consists of columnar or pyramidal cells with basal nuclei and densely packed granules which are negative for acidic mucus and positive for neutral mucus. In select MPGGs, there is a small amount of flocculent material in the lumen. The loss of acidic mucus production and the loss of traditional mucous glands are derived traits for Ensatina.