141 New Entities in the Order Chaetopeltidales

Two species of microfilamentous green algae are added to the Chaetopeltidales, one of which is new to science. The new taxon, to be placed in a new genus and species, is described from a freshwater environment in Argentina, and is placed in the Chaetopeltidales on the basis of its ultrastructural features. Thalli are prostrate, composed of radiating branched filaments that coalesce to form a disc. The pyrenoid is circled by starch plates and traversed by one or two convoluted cytoplasmic channels. The cell walls lack plasmodesmata. Asexual reproduction takes place by means of quadriflagellate zoospores released from central cells of the thallus. The absolute configuration of the zoospore flagellar apparatus is essentially identical to those of other chaetopeltidalean algae. Leptosiropsis torulosa Jao, 1937, isolated from New Zealand freshwaters, is placed in the Chaetopeltidales on the basis of its position in DNA sequence analyses. Thalli consist of erect branched filaments, the cells of which are connected by cross walls without plasmodesmata. The single large pyrenoid surrounds the nucleus. These are the first truly filamentous green algae to be included within the Chaetopeltidales.