Ultrastructural study of the type species of Peridiniopsis, Peridiniopsis borgei (Dinophyceae), with special reference to the peduncle and flagellar apparatus

Abstract

The general ultrastructure and flagellar apparatus of Peridiniopsis borgei were studied by serial section electron microscopy. The cells contained a conspicuous multiple-stalked pyrenoid in an anterior-dorsal position, relative to a large, central sac pusule (SP), and were surrounded by an unusual mucilage layer, located between the thecal plates and the outer amphiesmal membranes. The central SP was linked to the longitudinal flagellar canal by a narrow, 1.5 μm long tubular extension. An apical fibrous complex with three radiating fibres was associated with the apical pore complex. A flat peduncle emerged near the flagellar bases and was supported by a single row of 75–80 microtubules, which extended for nearly 50 μm along an elaborate path inside the cell. The flagellar apparatus resembled that of Peridinium cinctum but differences were noted. The layered connective was smaller and had fewer thin layers than that of P. cinctum. The microtubular root associated with the anterior surface of the transverse basal body nucleated a novel type of transverse microtubular root extension, in which 23 microtubules surrounding a fibrouscore extended along the surface of the SP. Two distinct fibres connected triplets of the transverse basal body to the longitudinal microtubular root (LMR). A large eyespot, located within chloroplast lobes, was found in the sulcal area. It differed from previously described dinoflagellate eyespots by having up to six layers of electron-opaque globules; the inner layers were intercalated among thylakoid lamellae. A vesicle containing a layer of crystal-like bodies was present between the ventral surface of the eyespot and the LMR. In all cells sectioned, a double unit membrane was located between the thecal plates and the cytoplasmic membrane.