THE MORPHOLOGY AND TAXONOMY OF THE PLANKTONIC DIATOM CHAETOCEROS COARCTATUS LAUDER (BACILLARIOPHYCEAE)

Abstract

The diatom Chaetoceros coarctatus has been studied by light (LM) and electron microscopy (SEM, TEM), from preserved plankton samples collected in the Gulf of California and off the Pacific coast of Baja California. Observations include the finding of a number of rimoportulae in a single valve (terminal or intercalary) and the difference in structure among the intercalary, anterior terminal and posterior terminal setae. The presence of more than one rimoportula in a single valve, and the possible function of the rimoportula in Chaetoceros raise interesting questions, which are matters of speculation at the moment. The characteristics of Ch. coarctatus lead me to propose a new section, Coarctata, within the subgenus Phaeoceros.