Abstract
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.
We acknowledge Dimitri Gorand (C2M, UPVD, F-Perpignan) and Elisabeth Sellier (CREMEM-Université Bordeaux I) for assistance with the SEM. We thank the USR 3278 (CNRS-EPHE) for funding diatom studies at Moorea Island and the CRIOBE-Moorea Team for valuable help in the field, particularly Franck Lerouvreur. Many thanks are also due to Pierre Compère (National Botanic Garden, Meise, Belgium) for revision of the Latin diagnosis and recommendation for the specific epithet spina-christi in place of antechristi. We wish to thank two anonymous reviewers for their helpful comments and Michel Poulin for his remarks and English improvement.
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