Ultrastructural features of leaf blade epidermal cells of the marine angiosperm Thalassodendron ciliatum (Forsk.) den Hartog are described. The cells resemble transfer cells since they possess a highly invaginated plasmalemma with which numerous mitochondria are often associated. However, wall ingrowths as known in transfer cells of terrestrial plants, are absent. The plasmalemma is investigated around loosely-distributed fibrillar material present within a labyrinthine extracytoplasmic space. This material differs from the material that comprises the cell walls. The cytoplasm of the cells is rich in ribosomes. As in epidermal cells of other marine angiosperms, chloroplasts feature prominently. Other cytoplasmic components include microbodies, lipid droplets, unusual membrane-bound spherical osmiophilic bodies, and relatively few microtubules, dictyosomes and ER profiles. A thin, but distinct cuticle covers the leaf surface. The outer tangential cell wall is about twice as thick as the other walls and has an interesting structure; the innermost portion of this wall often stains more intensely than the rest of the wall; wall striations, adjacent to this intensely-staining layer, are more prominent here than in the other walls; certain layers of the striated portion of the wall appear to have a porous texture; and cavities, generally similar to the subcuticular cavities of the marine angiosperm Zostera capensis Setchell, occur in the midregion of the wall, as well as beneath the cuticle. An extremely small opening is found in the cuticle that overlies a subcuticular cavity. The presence of an enlarged plasmalemma, a fenestrated cuticle and a partially porous outer wall suggests that these cells probably participate in absorptive and/or secretory or excretory processes.