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Abstract
The morphology and cell-cycle of the bipolar centric, marine diatom Odontella regia C. A. Agardh were studied, after establishing optimal growth conditions. The siliceous part of the cell wall is composed of loculate areolae with perforated sidewalls, which are internally attached to a system of parallel ribs arising from an elongated annulus. Two rimoportulae (RPs) are diagonally situated outside this primary band—i.e., the annulus. Their speedier and more massive silicification during morphogenesis causes a sigmoid distortion of the valve. Thickening of the wall occurs from outside to inside. There are 2 open girdle bands in the mature thecae.
The nucleus is suspended in the cell centre, with cytoplasmic strands attached mainly to the RPs, the horn-bases and to the last hypothecal band. Chloroplaste are restricted to the cortical cytoplasm. Preprophase is correlated with cell elongation and formation of the second hypothecal band. Pre- and postmitotic transapical nuclear migration, and the pattern of cleavage is comparable with the events in Biddulphiopsis titiana (Franz & Schmid 1994). Also, the reorientation, complete reduction and then new outgrowth of cytoplasmic strands is similar, but no diaphragm is formed. Post cytokinetic shaping of the cleavage furrow provides the mould for the gross morphology of the valve. Results are compared with those of B. titiana (Franz & Schmid 1994).