Tongue of the Egyptian Endemic Bridled Skink (Heremites vittatus; Olivier, 1804): Gross, Electron Microscopy, Histochemistry, and Immunohistochemical Analysis

SIMPLE SUMMARY: The present study describes the morphological characteristics of the tongue and laryngeal mound of Heremites vittatus. In SEM analysis, the complicated papillary system showed a special filiform system (nine subtypes) in addition to the conical system on the ventral surface of the foretongue apex. The dorsal surface of the laryngeal mound represented 18 longitudinal folds. Histologically, the keratinized layer was present in the foretongue but was absent in the mid- and hindtongue. Significant histochemical signals with positive glandular AB and PAS-positive reactions were observed. Immunohistochemistry showed strong cytokeratin immunopositivity in all parts of the tongue. ABSTRACT: The present study used light and scanning electron microscopy to describe the integrative morphological description of the tongue and laryngeal mound of Heremites vittatus, an endemic lizard of Saharan Africa. Additionally, ultrastructure, histology, histochemistry, and immunohistochemical approaches were used to characterize the lingual apparatus adaptations. In the present study, Heremites vittatus consisted of a complex lingual papillary system in which the ventral apical surface of the foretongue comprised conical papillae. The dorsal surface consisted of different filiform papillary (papillae filiformes) types: the anterior section had two types (bifid and pointed), and the posterior section had four types (triangular, trifid, quadrifid, and pentafid) papillae. The dorsal midtongue surface exhibits scale-like, serrated filiform papillae with anterior gland openings. The hindtongue consisted of two overlapping filiform papillae: scale-like, board-serrated papillae on the median portion and finger-like papillae on the wings. The dorsal surface of the laryngeal mound had 18 longitudinal folds with glandular openings. Histologically, the foretongue was covered by a slightly keratinized layer that was absent in the mid- and hindtongue. The lingual glands were absent from the foretongue but present in the interpapillary space in the mid- and hindtongues. We observed a few rounded taste buds in the conical papilla epithelium. Histochemical analysis revealed strong glandular Alcian Blue (AB)-positive and Periodic Acid–Schiff (PAS)-positive reactions. Immunohistochemistry showed strong cytokeratin immunopositivity in all parts of the tongue. In conclusion, the obtained data about the lingual characterizations have been consistent with the active foraging behavior of the species and its environmental conditions.