A new Cocconeis (Bacillariophyceae) from Moorea Island, Society Archipelago, South Pacific Ocean with distinctive valvocopula morphology and linking system

摘要

The study of coral reef diatoms on Moorea Island in the Society Archipelago, South Pacific Ocean revealed a strong representation of the Achnanthales, with many taxa of Cocconeis. One of these Cocconeis, examined by light and scanning electron microscopy, shows a sternum valve (SV) with a close resemblance to the Cocconeis scutellum lineage, whereas the raphe valve (RV) and the valvocopula system are different from that of C. scutellum, therefore a new name has been given to it, Cocconeis spina-christi sp. nov. This new taxon has several remarkable features: 1) the RV stria density is, on average, twice as high as that of the SV; 2) the RV valvocopula extended and structurally complex, has large marginal fenestrae, irregular digitiform fimbriae and one longer spine-like fimbria at each apex; and 3) an anchor system between the valvocopula of each valve is observed, consisting of a rounded papilla with transverse furrows lying on each basal RV valvocopula fimbria and fitting into a rounded concavity or cupule - in the corresponding marginal edge of the SV valvocopula. Such an anchor system between valvocopulae seems a characteristic common to several Cocconeis species bearing fimbriae on each valvocopula. The definition and limit of the concept of varieties in the C. scutellum lineage is also addressed.