Colony formation and valve morphology in the marine benthic diatom Dimeregramma fulvum

Abstract

Acid-cleaned cells of Dimeregramma fulvum collected from anchialine pools on Ascension Island were examined with light and scanning electron microscopy to elucidate their valve structure. Cells occur in zigzag-shaped colonies interconnected by mucus cushions, rather than forming ribbon-shaped colonies involving linking spines as seen in the type species of the genus, D. minor. Apical pore fields are the prominent feature of the valves. There is no evidence of rimoportulae present in the specimens examined. In light of the studies conducted thus far, we recognize two groups of species in the genus Dimeregramma, which differ in their valve morphology and thus in basic growth form. The characters used for their distinction are outlined.