Lingual ultrastructure of the long-finned pilot whale (Globicephala melas)

Microscopic studies on the cetacean tongue are limited and, to date, only a few ultrastructural reports on dolphins have been published. This report presents the initial description of the lingual ultrastructure of the long-finned pilot whale. The lingual integumental surface was smooth, lacking papillae, although flaking of outer stratum corneum cells could be observed at high resolution. The keratinocytes of the stratum spinosum of the epidermis resembled those of cetacean skin on other regions of the body. The similarities included the presence of cytoplasmic lipid droplets around the nuclei of stratutm spinosum cells, a lingual feature not seen in terrestrial mammals. Keratin intermediate filaments were numerous and occasionally formed aggregates of circular whorls. At cell surfaces, bundles of keratin intermediate filaments were frequently observed inserting into desmosomal plaques. Pigment granules were not evident and organelles were sparse. Stratum corneal cells contained nuclear remnants (parakeratosis) and small multivesicular bodies, and the corneal layer was approximately 18 cells thick. The nuclei of the stratum basale keratinocytes possessed exceptionally numerous and deep clefts. The dermis was nondistinctive. The skeletal muscle of the tongue was arranged in widely separated fasiculi containing small numbers of muscle fibres. Typical fine structure of skeletal muscle bands and tubular elements was observed by transmission electron microscopy.