The Morphology of the Tongue in the Spinner Dolphin (Stenella longirostris)

Assessments of the tongue morphology contribute to the understanding of evolutionary processes associated with food and feeding habits. In this sense, this study aimed to describe the tongue morphology in the Spinner dolphin (Stenella longirostris) and understand possible morphological associations with its food and feeding habits. Macroscopic dissections and light as well as scanning electron microscopy analyses of three Spinner dolphin tongues were performed. The tongues are elongated and exhibit a dorsal surface divided into three regions, namely the apex, the body and the root. Two types of lingual papillae, marginal and vallate papillae, were identified. Microscopically, the tongue is composed of a Tunica mucosa and a muscle layer, the Musculus lingualis proprius. The epithelial lining of the Tunica mucosa is a cornified stratified squamous epithelium. No taste buds were found in any of the identified lingual papillae. The Lamina propria mucosae is formed by loose and dense connective tissue and contains compound tubuloacinar glands with serous and mucous cells and the excretory ducts open on the lingual surface. Serous cells were positively stained by PAS, whereas mucous glands were positively stained by Alcian blue. The muscle layer is composed of striated muscle with longitudinal, transverse, and oblique bundles. Thus, Spinner dolphin tongues are similar to those of other odontocetes with only two types of lingual papillae and many lingual glands. Taste buds are absent. Based on the morphology, we hypothesize that the main function of the tongue in the Spinner dolphin is to aid in swallowing whole prey.