Fine Structure of the Dorsal Epithelium of the Tongue of the Japanese Terrapin, Clemmys japonica (Cheloia, Emydinae).

Abstract

Summary. As reptiles are situated phylogenetically between the amphibians and the mammals, they exhibit considerable variation in the structure of their tongues. The present study, one of a series of studies on reptile tongues, aims to demonstrate the three-dimensional structure of the dorsal lingual surface of a turtle, the Japanese terrapin Clemmys japonica, and to clarify the ultrastructural features of the lingual epithelial cells. In the study lingual papillae were observed by scanning electron microscopy to be widely distributed over the dorsal surface of the tongue. Irregularly shaped (conical, columnar or angular) papillae were located in the anterior and central areas, and ridge-like ones, in the latero-posterior area. Histological examination revealed that the connective tissue penetrated into the core of the papillae, and the epithelium was of a stratified squamous and/or cuboidal type. Under the transmission electron microscope, two types of cells were identified in the intermediate layer of the apical epithelium of the lingual papilla: one type was probably an immature mucous cell, whereas the other was elongated in a baso-apical direction, its cytoplasm containing fine granules. In the surface layer of the apical epithelium, typical mucous cells and cells containing numerous, fine, electron-lucent granules were recognized. Both types of cells possessed microvilli on their free-surfaces. In the lateral epithelium of the lingual papillae, the cytological features from the basal layer to the superficial intermediate layer were essentially the same as in the apical epithelium. However, in the surface layer, mucous cells were significantly larger in number than in the apical epithelium.In mammals, the tongue functions mainly for feeding (THEXTON, 1980) and for lapping (HIIEMAE et al., 1981). In some mammals, it also functions for the brushing of body hair. The relatively strong keratinization, especially of the dorsal epithelium, is associated with the performance of these functions. The keratinized epithelium forms compactly distributed fine processes or filiform papillae (FARBMAN, 1966(FARBMAN, , 1970CANE and SPEARMAN, 1969; HUME and POTTEN, 1976;BOSHELL et al., 1982;STEFLIK et al., 1983; MACKENZIE and BICKENBACH, 1984;IWASAKI andMIYATA, 1989, 1990; IWASAKI,1990a). In mammals, the tongue plays only a small part in the secretion of salivary fluid, as the major salivary glands develop to assume this purpose. By contrast, in amphibians, the tongue plays a very important role in the secretion of salivary fluid into the oral cavity, as well as in feeding (ZYLBERBERG, 1977; IWASAKI and WANICHANON,1991).Reptiles are situated phylogenetically between the amphibians and the mammals. There have been many macroscopic and light-microscopic studies on the tongues of reptiles (GNANAMUTHU, 1937;GOIN and GOIN, 1962;SMITH, 1984 SMITH, , 1986 SMITH, , 1988SCHWENK, 1986). The results of such studies have demonstrated considerable variation in the morphology and histology of the reptilial tongue. However, very few rep...

Fine structure of the dorsal lingual epithelium of the juvenile hawksbill turtle,Eretmochelys imbricata bissa

“…This difference might be related to the role of the lingual epithelium as a salivary gland. Almost all of the epithelial cells of the lingual dorsum of freshwater turtles contain mucous granules or other types of secretory granule (Iwasaki, 1992a;Iwasaki et al, 1992a), while those of the juvenile Hawskbill turtle do not contain any type of secretory granule.…”

“…The former animals live in or near ponds or small rivers while the latter are terrestrial. Iwasaki et al (1992a) postulated that the composition of the dorsal epithelium of the tongue might reflect an animal's environment. Thus, it is suggested that, when animals move from a freshwater to a terrestrial habitat, the dorsal lingual epithelium begins to lose secretory cells, which are replaced by stratified squamous cells.…”

“…These differences can be categorized phylogenetically and, at the same time, they reflect the adaptation of reptiles to their environments to a certain extent. For example, the lin-gual epithelium of completely terrestrial reptiles has a tendency to be karatinized (Mao et al, 1991;Iwasaki and Kumakura, 1994), while that of the reptiles that live in or near ponds or small rivers has a tendency to be nonkeratinized (Iwasaki, 1992a;Iwasaki et al, 1992a). The tongue of reptiles that live under amphibious circumstances tend to have both keratinized and nonkeratinized epithelia in different parts of the tongue (Schwenk, 1988;Iwasaki, 1990;Iwasaki and Kobayashi, 1992).…”

Ultrastructural Studies on the Tongue of Some Egyptian Lizards 1-Scincine Lizards Chalcides Oscellatus and Chalcides Sepsoides (Lacertilia, Scincidae)

“…Numerous investigators concluded that tongue of most tetrapods are provided with voluntary and movable muscles [4][5][6][7][8][9][10][11]. Reptilian tongues are characterized by morphological and functional variations among species [12][13][14].…”

The dorsal lingual epithelium of Rhinoclemmys pulcherrima incisa (Chelonia, Cryptodira)

“…Within chelonians, the outline of the tongue, the dorsal tongue topography, and the presence, form, and distribution of lingual papillae show significant variability (Winokur, 1988;Weisgram et al, 1989;Iwasaki, 1992;Iwasaki et al, 1992Iwasaki et al, , 1996aBeisser et al, 1995Beisser et al, , 1998Beisser et al, , 2001). There are substantial differences in the lingual epithelium of turtles, possibly reflecting the adaptation of turtles to their diet and the different environments (water and/or land) where feeding occurs (Winokur, 1973(Winokur, , 1988: In an aquatic environment, a tongue would be a hindrance when using water as the main mechanism for food uptake (Bramble and Wake, 1985).…”