Morphology and phylogeny of four species from the genus Bacteriastrum (Bacillariophyta)

Four colonial species of the multipolar centric diatom genus Bacteriastrum– B. furcatum, B. hyalinum, B. jadranum and B. mediterraneum – were investigated using field samples from the Adriatic Sea and cultured strains obtained from these samples. Morphology and frustuleultrastructure were examined using light and electron microscopy, and nuclear-encoded large-subunit (LSU) rDNA sequences were obtained from the strains. The description of B. jadranum has been emended based on a novel mechanism of colony formation in Bacteriastrumin which cells are joined through an organic cell jacket which holds together cells in chains. Descriptions for two of the three other species were supplemented; vegetative cells of B. hyalinum have short Y spinuleson the fused part of the setaeand T-shaped outgrowths, and the spores of this species possess a ring of puncta and a granular surface on the exterior side of the primary valve mantle. Specific for B. furcatum is the location of pores scattered around the setaebases...