MORPHOLOGICAL VARIATION OF THE ATTACHED DIATOM:COCCONEIS SCUTELLUMVAR.SCUTELLUM: (BACILLARIOPHYCEAE)1

Abstract

ABSTRACTThe morphology and sexual reproduction of the attached diatom Cocconeis scutellum Ehr. var. scutellum have been investigated using field and culture materials. The diatom grew well at 14–22° C and in a medium using enriched full strength seawater or 50% diluted seawater. One gamete was formed without cytokinesis in a gametangium and one auxospore arose from paired gametangia. The size of gametangia and initial cells were 17.8–29.9 μm and 43.3–59.5 μm, respectively. Valve width decreased linearly with decreasing valve length. The regression coefficient between them was invariable with the change of the environment. The transapical striation densities were 7–12 and 7.5–13.5 in 10 μm in araphid and raphid valves, respectively. The density showed a tendency to increase with decreasing valve length in both valves. The densities in both valves, except the small araphid valve, are invariable with the change of the environment. The relationships between valve length and width, and between valve length and striation density have been compared with those of taxa allied to C. scutellum var. scutellum. It is concluded that C. scutellum var. scutellum, as usually delimited, is a heterogenous taxon.