Andersenia, a genus of filamentous, sand-dwelling Pelagophyceae from southeastern Australia

Abstract

:A new marine pelagophyte genus, Andersenia, was described from clonal cultures established from sand samples collected in coastal tide pools from southeastern Australia. Thin, uniseriate, unbranched filaments were variable in length up to 1.0 mm, 7–12 μm in width and surrounded by a gelatinous envelope. Cells contained one or two golden brown, lobed chloroplasts. Growing filaments often segmented into fragments of varying length that were continuous within the filament envelope and eventually produced multicellular knots, giving mature filaments a gnarled appearance. Most vegetative cells generated asexual motile zoospores that were heterokont with two unequal, heterodynamic flagella that arose together approximately one-third the length of the cell from the anterior surface; one or two lobed chloroplasts were located towards the posterior of the cells, while numerous granules of uniform size were typically obvious at the cell periphery. During segmentation, zoospore formation and release, the unusual cross walls shaped like biconcave discs were revealed and were characteristic of the genus. Zoospores adhered and secreted an adhesive pad within minutes of attachment and initiated new filaments. Phylogenetic analysis based on the nuclear-encoded small subunit ribosomal RNA (SSU rRNA) as well as morphological differences placed the new genus Andersenia in the class Pelagophyceae, and the three strains studied formed two species, A. nodulosa sp. nov. and A. australica sp. nov. Andersenia nodulosa filaments were longer and the cells smaller than in A. australica, and they differed by 16 nucleotides (99.2% identity) at the SSU rRNA sequence level.