Microstructure of the Surface of the Tongue and Histochemical Study of the Lingual Glands of the Lowland Tapir (Tapirus terrestris Linnaeus, 1758) (Perissodactyla: Tapiridae)

SIMPLE SUMMARY: This is a detailed study of the surface morphology of the tongue and the lingual glands of the lowland tapir (Tapirus terrestris), which expands the understanding of the adaptation of this species to habitats. The histological and ultrastructural analysis of the lingual papillae and lingual glands revealed the presence of two types of mechanical papillae, namely the filiform and conical papillae, while papillae with taste buds (including the fungiform papillae, vallate papillae, and foliate papillae) formed the second, less numerous group. The filiform papillae differed from those of Equidae or Rhinocerotidae. The presence of nine vallate papillae, localized in groups of two surrounded by a ring, or individually, was unique for the examined female tapir. In addition, the vallate papillae contained irregular pseudopapillae on their surface. The foliate papillae contained several sulci between each folia. The presence of sparse taste buds in the side wall of the vallate papillae and foliate papillae is unique for the tapir. Compared to other Perissodactyla, the number of taste buds in the tapir is limited, although the features of its tongue surface make it possible to distinguish this species from representatives of Equidae or Rhinocerotidae. ABSTRACT: Although the anatomy of the gastrointestinal tract has been characterized in the lowland tapir (Tapirus terrestris), the exact anatomy of its tongue has not been studied. Samples of the lingual papillae and lingual glands were collected from the tongue of an adult female lowland tapir. The microscopic analysis of the structure of the lingual papillae and the histochemical analysis of the secretion of the lingual glands were analyzed. The tongue of the tapir is divided into the apex, body with a distinct lingual prominence, and the root. Its ventral surface is smooth. The most numerous of the mechanical papillae were the filiform papillae, while numerous conical papillae with a sharp apex or more rounded papillae were present in the root of the tongue. There were also nine vallate papillae and pair of foliate papillae. The foliate papillae contained several folds parted by 12–14 grooves. The mucous secretion produced by the lingual glands was more obvious than the serous secretion. The features of the dorsal surface of the tongue as well as the shape and number of the lingual papillae on the surface of the tongue of the examined female tapir differ compared to Equidae or Rhinocerotidae, the other two representatives of Perissodactyla. However, further study is necessary for the synapomorpy of the tapir’s tongue.