HISTOLOGICAL AND ULTRASTRUCTURAL-STUDY OF THE LINGUAL EPITHELIUM OF THE JUVENILE PACIFIC RIDLEY TURTLE, LEPIDOCHELYS OLIVACEA (CHELONIA, CHELONIIDAE)

Histological and ultrastructural studies ot the dorsal lingual epithel ium of the juvenile Pacific ridley turtle, Lepidochelys olivacea, were performed by light and electron microscopy, and the results were comp ared to those of freshwater turtles in order to clarify the relationsh ip between the histological and cellular differences of the lingual ep ithelium and the habitat of the turtles. The tongue of the juvenile Pa cific ridley turtle is triangular with a round apex when viewed from a bove, but it appears flattened in lateral view. Scanning electron micr oscopy (SEM) revealed no lingual papillae on the dorsal surface of the tongue. Instead, transverse plicae are found on the surface of the bo dy and the radix. The surface of the apex is smooth. Microridge-like s tructures are present on the surfaces of the cells, and the cell margi ns are thickened. The mucosal epithelium is keratinized, stratified sq uamous with a relatively thick layer of desquamating cells. Cells of t he basal and deep intermediate layers appear elliptical in shape; and their nuclei are elliptical and centrally located. Numerous desmosomes join the processes of adjacent cells; and hemidesmosomes anchor the b asal cells to the basal lamina. The cytoplasm of these cells contains mitochondria, free ribosomes, rough endoplasmic reticulum, vacuoles, a nd bundles of tonofilaments. Cells and their nuclei in the intermediat e layer display gradual flattening. In the shallow intermediate layer, the cells are significantly flattened, with nuclei condensed or absen t. The cytoplasm contains many tonofibrils or bundles of tonofilaments , free ribosomes and keratohyalin granules, with numerous ribosomes at tached to their surfaces. A few collapsed mitochondria are visible. Ce ll membranes of the shallow intermediate cells are smooth and attached to those of adjacent cells by desmosomes. The keratinized layer is lo cated on top of the shallow intermediate layer, and consists of signif icantly flattened cells lacking nuclei and filled with keratin fibers. Very fine cellular processes joined by desmosomes are visible. The de squamating cells located on top of the keratinized layer contain kerat in fibers that are somewhat thicker than tonofibrils and tonofilaments , and clearly distinguishable individually. The microridge-like struct ures visible by SEM could be attributed to the persistence of cells fo rmed in underlying layer. In conclusion, the histology of the lingual epithelium of the juvenile Pacific ridley turtle differs significantly from that of the adult freshwater turtle in spite of the similarity o f the gross morphology of their tongues.