Morphology and formal description of Sellaphora bisexualis sp. nov. (Bacillariophyta)

Abstract

Previous molecular genetic and life cycle studies have revealed the existence of a vigorously homothallic deme within the Sellaphora pupula species complex, which was given the provisional name of Sellaphora [pupula K-LB] Φ 'urban elliptical'. This is described here as S. bisexualis sp. nov., with a cox1 DNA-barcoded type from Scotland. A detailed description of frustule ultrastructure is given, the most complete for a Sellaphora species. The morphology of the terminal raphe fissure is variable, becoming vestigial in some small pre-auxospore valves, and the boundary between the raphe-sternum and striae is sometimes strongly, sometimes weakly marked by larger areolae and an external groove. The cingulum contains at least three plain bands. The pars interior of band 1 (the valvocopula), as well as being undulate with a pitch corresponding to the transapical ribs, bears a very fine fringe of short fimbriae. Sexual reproduction involves 'male' and 'female' gametangia, as in other allogamous species of Sellaphora, but in S. bisexualis cells of the same clone can differentiate into either sex, allowing homothallic reproduction and successive inbred generations. The proven distribution of the species includes sites in the UK and Australia. © Czech Phycological Society.