Ultrastructure of Stylodinium Iittorale (Dinophyceae) with special reference to the stalk and apical stalk complex

Abstract

SUMMARYThe ultrastructure of Stylodinium littorale Horiguchi et Chihara, a marine, sand‐dwelling coccoid dinoflagel‐late, was investigated with special emphasis on its stalk and the apical stalk complex. The dinoflagellate alternates between non‐motile and motile cells in its life cycle. The non‐motile cell possesses a long and distinct stalk. The stalk, consisting of a main cylindrical part and a holdfast, is firmly attached to a thecal plate (the apical pore plate). A part of its proximal portion is hollow and V‐shaped in section. The V‐shaped hollow space is underlain by a projection from the apical pore plate. An apical stalk complex is present in the motile cells and consists of a large apical pore plate and mucilaginous material. The apical pore plate is depressed into the cell, but has a narrow central tubular projection. The mucilaginous stalk‐building material is stored between this plate and the outer plate membrane. The tubular projection of the apical pore plate corresponds to the apical pore of other dinoflagellates and its lumen is filled with electron‐dense material. The structure of the apical stalk complex is compared with the homologous structure in Bysmatrum arenicola, the only other example of an apical stalk complex that has been investigated. A general ultrastructural survey revealed that S. littorale possesses a typical dinoflagellate cellular structure.